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Java | All Algorithms implemented in Java | Learning library

 by   TheAlgorithms Java Version: Current License: MIT

 by   TheAlgorithms Java Version: Current License: MIT

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kandi X-RAY | Java Summary

Java is a Java library typically used in Tutorial, Learning, Example Codes, LeetCode applications. Java has no bugs, it has no vulnerabilities, it has build file available, it has a Permissive License and it has medium support. You can download it from GitHub.
You can run and edit the algorithms, or contribute to them using Gitpod.io (a free online development environment) with a single click.
Support
Support
Quality
Quality
Security
Security
License
License
Reuse
Reuse

kandi-support Support

  • Java has a medium active ecosystem.
  • It has 45287 star(s) with 14850 fork(s). There are 2275 watchers for this library.
  • It had no major release in the last 12 months.
  • There are 5 open issues and 614 have been closed. On average issues are closed in 24 days. There are 11 open pull requests and 0 closed requests.
  • It has a neutral sentiment in the developer community.
  • The latest version of Java is current.
Java Support
Best in #Learning
Average in #Learning
Java Support
Best in #Learning
Average in #Learning

quality kandi Quality

  • Java has 0 bugs and 0 code smells.
Java Quality
Best in #Learning
Average in #Learning
Java Quality
Best in #Learning
Average in #Learning

securitySecurity

  • Java has no vulnerabilities reported, and its dependent libraries have no vulnerabilities reported.
  • Java code analysis shows 0 unresolved vulnerabilities.
  • There are 0 security hotspots that need review.
Java Security
Best in #Learning
Average in #Learning
Java Security
Best in #Learning
Average in #Learning

license License

  • Java is licensed under the MIT License. This license is Permissive.
  • Permissive licenses have the least restrictions, and you can use them in most projects.
Java License
Best in #Learning
Average in #Learning
Java License
Best in #Learning
Average in #Learning

buildReuse

  • Java releases are not available. You will need to build from source code and install.
  • Build file is available. You can build the component from source.
  • Java saves you 5400 person hours of effort in developing the same functionality from scratch.
  • It has 22301 lines of code, 1866 functions and 415 files.
  • It has medium code complexity. Code complexity directly impacts maintainability of the code.
Java Reuse
Best in #Learning
Average in #Learning
Java Reuse
Best in #Learning
Average in #Learning
Top functions reviewed by kandi - BETA

kandi has reviewed Java and discovered the below as its top functions. This is intended to give you an instant insight into Java implemented functionality, and help decide if they suit your requirements.

  • Finds the closest location in the given array of coordinates .
    • Checks if the given binary tree is balanced .
      • Multiply two integers
        • Remove a node .
          • Calculates the page rank .
            • Generates a vertical traversal of the tree .
              • Entry point to interactive mode
                • Calculates the max of an array .
                  • Checks if a system is still in a safe state .
                    • Returns minimum number of cuts required for a substring .

                      Get all kandi verified functions for this library.

                      Get all kandi verified functions for this library.

                      Java Key Features

                      All Algorithms implemented in Java

                      How do purely functional languages handle index-based algorithms?

                      copy iconCopydownload iconDownload
                      prefixList = scanl1 (+)
                      
                      Prelude> prefixList [1 .. 9]
                      [1,3,6,10,15,21,28,36,45]
                      
                      prefixList = scanl1 (+)
                      
                      Prelude> prefixList [1 .. 9]
                      [1,3,6,10,15,21,28,36,45]
                      
                      > scanl (+) 0 [1..9]
                      [0,1,3,6,10,15,21,28,36,45]
                      
                      scanl :: (b -> a -> b) -> b -> [a] -> [b]
                      scanl _ q [] = [q]
                      scanl f a (b:xs) = a : scanl f (f a b) xs
                      
                      > scanl (+) 0 [1..9]
                      [0,1,3,6,10,15,21,28,36,45]
                      
                      scanl :: (b -> a -> b) -> b -> [a] -> [b]
                      scanl _ q [] = [q]
                      scanl f a (b:xs) = a : scanl f (f a b) xs
                      
                      (define (prefix-stream s)
                        (let ps-loop ([st s]
                                      [p 0])
                          (if (stream-empty? st)
                              empty-stream
                              (let ([np (+ p (stream-first st))])
                                (stream-cons 
                                    np 
                                    (ps-loop 
                                        (stream-rest st)
                                        np))))))
                      
                      > (stream->list (prefix-stream (in-range 1 10)))
                      '(1 3 6 10 15 21 28 36 45)
                      
                      > (prefix-stream (in-naturals))
                      #<stream>
                      
                      (stream->list (stream-take (prefix-stream (in-naturals)) 10))
                      '(0 1 3 6 10 15 21 28 36 45)
                      > (stream->list (stream-take (stream-tail (prefix-stream (in-naturals)) 1000) 10))
                      '(500500 501501 502503 503506 504510 505515 506521 507528 508536 509545)
                      
                      (define (prefix-stream s)
                        (let ps-loop ([st s]
                                      [p 0])
                          (if (stream-empty? st)
                              empty-stream
                              (let ([np (+ p (stream-first st))])
                                (stream-cons 
                                    np 
                                    (ps-loop 
                                        (stream-rest st)
                                        np))))))
                      
                      > (stream->list (prefix-stream (in-range 1 10)))
                      '(1 3 6 10 15 21 28 36 45)
                      
                      > (prefix-stream (in-naturals))
                      #<stream>
                      
                      (stream->list (stream-take (prefix-stream (in-naturals)) 10))
                      '(0 1 3 6 10 15 21 28 36 45)
                      > (stream->list (stream-take (stream-tail (prefix-stream (in-naturals)) 1000) 10))
                      '(500500 501501 502503 503506 504510 505515 506521 507528 508536 509545)
                      
                      (define (prefix-stream s)
                        (let ps-loop ([st s]
                                      [p 0])
                          (if (stream-empty? st)
                              empty-stream
                              (let ([np (+ p (stream-first st))])
                                (stream-cons 
                                    np 
                                    (ps-loop 
                                        (stream-rest st)
                                        np))))))
                      
                      > (stream->list (prefix-stream (in-range 1 10)))
                      '(1 3 6 10 15 21 28 36 45)
                      
                      > (prefix-stream (in-naturals))
                      #<stream>
                      
                      (stream->list (stream-take (prefix-stream (in-naturals)) 10))
                      '(0 1 3 6 10 15 21 28 36 45)
                      > (stream->list (stream-take (stream-tail (prefix-stream (in-naturals)) 1000) 10))
                      '(500500 501501 502503 503506 504510 505515 506521 507528 508536 509545)
                      
                      (define (prefix-stream s)
                        (let ps-loop ([st s]
                                      [p 0])
                          (if (stream-empty? st)
                              empty-stream
                              (let ([np (+ p (stream-first st))])
                                (stream-cons 
                                    np 
                                    (ps-loop 
                                        (stream-rest st)
                                        np))))))
                      
                      > (stream->list (prefix-stream (in-range 1 10)))
                      '(1 3 6 10 15 21 28 36 45)
                      
                      > (prefix-stream (in-naturals))
                      #<stream>
                      
                      (stream->list (stream-take (prefix-stream (in-naturals)) 10))
                      '(0 1 3 6 10 15 21 28 36 45)
                      > (stream->list (stream-take (stream-tail (prefix-stream (in-naturals)) 1000) 10))
                      '(500500 501501 502503 503506 504510 505515 506521 507528 508536 509545)
                      
                      (defn prefix-list [nums]
                        (loop [i 1
                               prefix nums]
                          (if (= i (count nums))
                            prefix
                            (recur (inc i) (assoc prefix i (+ (get prefix i) (get prefix (dec i))))))))
                      
                      from itertools import accumulate
                      print(list(accumulate(range(1, 10))))
                      
                      nums = np.array([1, 2, 3, 4, 5, 6, 7, 8, 9]) # or np.arange(1, 10) or np.arange(9)+1
                      print(nums.cumsum())
                      
                      [1, 3, 6, 10, 15, 21, 28, 36, 45]
                      
                      nums = np.array([1, 2, 3, 4, 5, 6, 7, 8, 9]) # or np.arange(1, 10) or np.arange(9)+1
                      print(nums.cumsum())
                      
                      [1, 3, 6, 10, 15, 21, 28, 36, 45]
                      
                      Enum.scan(1..9, 0, fn element, acc -> element + acc end) |> IO.inspect()
                      # yields:
                      # [1, 3, 6, 10, 15, 21, 28, 36, 45]
                      
                      defmodule Foo do
                        def bar(nums, acc \\ [])
                      
                        # We've reached the end of input: return the accumulator (reversed)
                        def bar([], acc), do: Enum.reverse(acc)
                      
                        # The very first call is special because we do not have a previous value
                        def bar([x | tail], []) do
                          bar(tail, [x])
                        end
                      
                        # All other calls land here
                        def bar([x | tail], [prev | _] = acc) do
                          bar(tail, [x + prev | acc])
                        end
                      end
                      
                      
                      nums =   [1, 2, 3, 4,  5,  6,  7,  8,  9]
                      prefix = Foo.bar(nums)
                      IO.inspect(prefix)
                      
                      # Yields the same result:
                      # [1, 3, 6, 10, 15, 21, 28, 36, 45]
                      
                      Enum.scan(1..9, 0, fn element, acc -> element + acc end) |> IO.inspect()
                      # yields:
                      # [1, 3, 6, 10, 15, 21, 28, 36, 45]
                      
                      defmodule Foo do
                        def bar(nums, acc \\ [])
                      
                        # We've reached the end of input: return the accumulator (reversed)
                        def bar([], acc), do: Enum.reverse(acc)
                      
                        # The very first call is special because we do not have a previous value
                        def bar([x | tail], []) do
                          bar(tail, [x])
                        end
                      
                        # All other calls land here
                        def bar([x | tail], [prev | _] = acc) do
                          bar(tail, [x + prev | acc])
                        end
                      end
                      
                      
                      nums =   [1, 2, 3, 4,  5,  6,  7,  8,  9]
                      prefix = Foo.bar(nums)
                      IO.inspect(prefix)
                      
                      # Yields the same result:
                      # [1, 3, 6, 10, 15, 21, 28, 36, 45]
                      

                      Springboot 2.6.0 / Spring fox 3 - Failed to start bean 'documentationPluginsBootstrapper'

                      copy iconCopydownload iconDownload
                      @SpringBootApplication
                      @EnableSwagger2
                      public class Application {
                      
                      // build.gradle
                      implementation "org.springdoc:springdoc-openapi-ui:1.6.4"
                      
                      @SpringBootApplication
                      @OpenAPIDefinition
                      public class MyApplication {
                          public static void main(String[] args) {
                              SpringApplication.run(MyApplication.class, args);
                          }
                      }
                      
                      // build.gradle
                      implementation "org.springdoc:springdoc-openapi-ui:1.6.4"
                      
                      @SpringBootApplication
                      @OpenAPIDefinition
                      public class MyApplication {
                          public static void main(String[] args) {
                              SpringApplication.run(MyApplication.class, args);
                          }
                      }
                      
                      @Bean
                      public WebMvcEndpointHandlerMapping webEndpointServletHandlerMapping(WebEndpointsSupplier webEndpointsSupplier, ServletEndpointsSupplier servletEndpointsSupplier, ControllerEndpointsSupplier controllerEndpointsSupplier, EndpointMediaTypes endpointMediaTypes, CorsEndpointProperties corsProperties, WebEndpointProperties webEndpointProperties, Environment environment) {
                              List<ExposableEndpoint<?>> allEndpoints = new ArrayList();
                              Collection<ExposableWebEndpoint> webEndpoints = webEndpointsSupplier.getEndpoints();
                              allEndpoints.addAll(webEndpoints);
                              allEndpoints.addAll(servletEndpointsSupplier.getEndpoints());
                              allEndpoints.addAll(controllerEndpointsSupplier.getEndpoints());
                              String basePath = webEndpointProperties.getBasePath();
                              EndpointMapping endpointMapping = new EndpointMapping(basePath);
                              boolean shouldRegisterLinksMapping = this.shouldRegisterLinksMapping(webEndpointProperties, environment, basePath);
                              return new WebMvcEndpointHandlerMapping(endpointMapping, webEndpoints, endpointMediaTypes, corsProperties.toCorsConfiguration(), new EndpointLinksResolver(allEndpoints, basePath), shouldRegisterLinksMapping, null);
                          }
                      
                      
                      private boolean shouldRegisterLinksMapping(WebEndpointProperties webEndpointProperties, Environment environment, String basePath) {
                              return webEndpointProperties.getDiscovery().isEnabled() && (StringUtils.hasText(basePath) || ManagementPortType.get(environment).equals(ManagementPortType.DIFFERENT));
                          }
                      
                      @EnableSwagger2
                      @SpringBootApplication
                      @EnableSwagger2
                      public class Application {}
                      
                      @EnableWebMvc
                      @SpringBootApplication
                      public class MyApp {
                          public static void main(String[] args) {
                              SpringApplication.run(MyApp.class);
                          }
                      }
                      
                      @Bean
                          public WebMvcRequestHandlerProvider webMvcRequestHandlerProvider(Optional<ServletContext> servletContext, HandlerMethodResolver methodResolver, List<RequestMappingInfoHandlerMapping> handlerMappings) {
                              handlerMappings = handlerMappings.stream().filter(rh -> rh.getClass().getName().contains("RequestMapping")).toList();
                              return new WebMvcRequestHandlerProvider(servletContext, methodResolver, handlerMappings);
                          }
                      

                      Your project requires a newer version of the Kotlin Gradle plugin. (Android Studio)

                      copy iconCopydownload iconDownload
                      classpath 'com.android.tools.build:gradle:4.1.0'
                      
                      distributionUrl=https\://services.gradle.org/distributions/gradle-6.7.1-bin.zip
                      
                      classpath 'com.android.tools.build:gradle:4.1.0'
                      
                      distributionUrl=https\://services.gradle.org/distributions/gradle-6.7.1-bin.zip
                      
                      buildscript {
                          ext.kotlin_version = '1.6.10' // Change here
                          repositories {
                              google()
                              jcenter()
                          }
                      
                          dependencies {
                              classpath 'com.android.tools.build:gradle:4.1.0'
                              classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
                          }
                      }
                      
                      Incompatible classes were found in dependencies. Remove them from the classpath or use '-Xskip-metadata-version-check' to suppress errors
                      e: /home/user/.gradle/caches/transforms-3/36814238b86d8b6b6f9e4e1263bce879/transformed/jetified-kotlinx-coroutines-core-jvm-1.5.2.jar!/META-INF/kotlinx-coroutines-core.kotlin_module: 
                      Module was compiled with an incompatible version of Kotlin. 
                      The binary version of its metadata is 1.5.1, expected version is 1.1.15.
                      
                      buildscript {
                          ext.kotlin_version = '1.6.10' // Change here
                          repositories {
                              google()
                              jcenter()
                          }
                      
                          dependencies {
                              classpath 'com.android.tools.build:gradle:4.1.0'
                              classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
                          }
                      }
                      
                      Incompatible classes were found in dependencies. Remove them from the classpath or use '-Xskip-metadata-version-check' to suppress errors
                      e: /home/user/.gradle/caches/transforms-3/36814238b86d8b6b6f9e4e1263bce879/transformed/jetified-kotlinx-coroutines-core-jvm-1.5.2.jar!/META-INF/kotlinx-coroutines-core.kotlin_module: 
                      Module was compiled with an incompatible version of Kotlin. 
                      The binary version of its metadata is 1.5.1, expected version is 1.1.15.
                      
                      ext.kotlin_version = '<latest-version>'
                      
                      Execution failed for task ':assets_audio_player:compileDebugKotlin'.
                      
                      ext.kotlin_version = '<latest-version>'
                      
                      Execution failed for task ':assets_audio_player:compileDebugKotlin'.
                      
                      ext.kotlin_version = '1.6.10' //
                      
                       buildscript {
                      ext.kotlin_version = '1.6.10'
                      repositories {
                          google()
                          mavenCentral()
                      }
                      

                      Unable to load class AndroidComponentsExtension after upgrading the Android Gradle Plugin 7.1

                      copy iconCopydownload iconDownload
                      Caused by: java.lang.NoClassDefFoundError: com/android/build/api/extension/AndroidComponentsExtension
                          at androidx.navigation.safeargs.gradle.SafeArgsPlugin.apply(SafeArgsPlugin.kt:73)
                          at androidx.navigation.safeargs.gradle.SafeArgsPlugin.apply(SafeArgsPlugin.kt:42)
                      
                      dependencies {
                          classpath 'com.android.tools.build:gradle:7.1.0'
                      
                          // Update this line to use 2.4.1
                          classpath "androidx.navigation:navigation-safe-args-gradle-plugin:2.4.1"
                      }
                      
                      classpath "com.google.firebase:perf-plugin:1.4.0"
                      
                      Caused by: java.lang.NoClassDefFoundError: com/android/build/api/extension/AndroidComponentsExtension
                          at com.google.firebase.perf.plugin.FirebasePerfClassVisitorFactory.registerForProject(FirebasePerfClassVisitorFactory.java:54)
                          at com.google.firebase.perf.plugin.FirebasePerfPlugin.perform(FirebasePerfPlugin.java:145)
                          at com.google.firebase.perf.plugin.FirebasePerfPlugin.lambda$apply$0(FirebasePerfPlugin.java:107)
                      
                      classpath "com.google.firebase:perf-plugin:1.4.1"
                      
                      Caused by: java.lang.NoClassDefFoundError: com/android/build/api/extension/AndroidComponentsExtension
                          at androidx.navigation.safeargs.gradle.SafeArgsPlugin.apply(SafeArgsPlugin.kt:73)
                          at androidx.navigation.safeargs.gradle.SafeArgsPlugin.apply(SafeArgsPlugin.kt:42)
                      
                      dependencies {
                          classpath 'com.android.tools.build:gradle:7.1.0'
                      
                          // Update this line to use 2.4.1
                          classpath "androidx.navigation:navigation-safe-args-gradle-plugin:2.4.1"
                      }
                      
                      classpath "com.google.firebase:perf-plugin:1.4.0"
                      
                      Caused by: java.lang.NoClassDefFoundError: com/android/build/api/extension/AndroidComponentsExtension
                          at com.google.firebase.perf.plugin.FirebasePerfClassVisitorFactory.registerForProject(FirebasePerfClassVisitorFactory.java:54)
                          at com.google.firebase.perf.plugin.FirebasePerfPlugin.perform(FirebasePerfPlugin.java:145)
                          at com.google.firebase.perf.plugin.FirebasePerfPlugin.lambda$apply$0(FirebasePerfPlugin.java:107)
                      
                      classpath "com.google.firebase:perf-plugin:1.4.1"
                      
                      Caused by: java.lang.NoClassDefFoundError: com/android/build/api/extension/AndroidComponentsExtension
                          at androidx.navigation.safeargs.gradle.SafeArgsPlugin.apply(SafeArgsPlugin.kt:73)
                          at androidx.navigation.safeargs.gradle.SafeArgsPlugin.apply(SafeArgsPlugin.kt:42)
                      
                      dependencies {
                          classpath 'com.android.tools.build:gradle:7.1.0'
                      
                          // Update this line to use 2.4.1
                          classpath "androidx.navigation:navigation-safe-args-gradle-plugin:2.4.1"
                      }
                      
                      classpath "com.google.firebase:perf-plugin:1.4.0"
                      
                      Caused by: java.lang.NoClassDefFoundError: com/android/build/api/extension/AndroidComponentsExtension
                          at com.google.firebase.perf.plugin.FirebasePerfClassVisitorFactory.registerForProject(FirebasePerfClassVisitorFactory.java:54)
                          at com.google.firebase.perf.plugin.FirebasePerfPlugin.perform(FirebasePerfPlugin.java:145)
                          at com.google.firebase.perf.plugin.FirebasePerfPlugin.lambda$apply$0(FirebasePerfPlugin.java:107)
                      
                      classpath "com.google.firebase:perf-plugin:1.4.1"
                      
                      Caused by: java.lang.NoClassDefFoundError: com/android/build/api/extension/AndroidComponentsExtension
                          at androidx.navigation.safeargs.gradle.SafeArgsPlugin.apply(SafeArgsPlugin.kt:73)
                          at androidx.navigation.safeargs.gradle.SafeArgsPlugin.apply(SafeArgsPlugin.kt:42)
                      
                      dependencies {
                          classpath 'com.android.tools.build:gradle:7.1.0'
                      
                          // Update this line to use 2.4.1
                          classpath "androidx.navigation:navigation-safe-args-gradle-plugin:2.4.1"
                      }
                      
                      classpath "com.google.firebase:perf-plugin:1.4.0"
                      
                      Caused by: java.lang.NoClassDefFoundError: com/android/build/api/extension/AndroidComponentsExtension
                          at com.google.firebase.perf.plugin.FirebasePerfClassVisitorFactory.registerForProject(FirebasePerfClassVisitorFactory.java:54)
                          at com.google.firebase.perf.plugin.FirebasePerfPlugin.perform(FirebasePerfPlugin.java:145)
                          at com.google.firebase.perf.plugin.FirebasePerfPlugin.lambda$apply$0(FirebasePerfPlugin.java:107)
                      
                      classpath "com.google.firebase:perf-plugin:1.4.1"
                      
                      Caused by: java.lang.NoClassDefFoundError: com/android/build/api/extension/AndroidComponentsExtension
                          at androidx.navigation.safeargs.gradle.SafeArgsPlugin.apply(SafeArgsPlugin.kt:73)
                          at androidx.navigation.safeargs.gradle.SafeArgsPlugin.apply(SafeArgsPlugin.kt:42)
                      
                      dependencies {
                          classpath 'com.android.tools.build:gradle:7.1.0'
                      
                          // Update this line to use 2.4.1
                          classpath "androidx.navigation:navigation-safe-args-gradle-plugin:2.4.1"
                      }
                      
                      classpath "com.google.firebase:perf-plugin:1.4.0"
                      
                      Caused by: java.lang.NoClassDefFoundError: com/android/build/api/extension/AndroidComponentsExtension
                          at com.google.firebase.perf.plugin.FirebasePerfClassVisitorFactory.registerForProject(FirebasePerfClassVisitorFactory.java:54)
                          at com.google.firebase.perf.plugin.FirebasePerfPlugin.perform(FirebasePerfPlugin.java:145)
                          at com.google.firebase.perf.plugin.FirebasePerfPlugin.lambda$apply$0(FirebasePerfPlugin.java:107)
                      
                      classpath "com.google.firebase:perf-plugin:1.4.1"
                      
                      // Top-level build file where you can add configuration options common to all sub-projects/modules.
                      plugins {
                          id 'com.android.application' version '7.1.0' apply false
                          id 'com.android.library' version '7.1.0' apply false
                          id 'org.jetbrains.kotlin.android' version '1.6.10' apply false
                          id "com.google.dagger.hilt.android" version '2.41' apply false
                          id 'androidx.navigation.safeargs.kotlin' version '2.4.0' apply false // use this one
                      //    classpath "androidx.navigation:navigation-safe-args-gradle-plugin:2.4.0" (will not work now)
                      
                      }
                      
                      task clean(type: Delete) {
                          delete rootProject.buildDir
                      }
                      
                      I fixed the issue by downgrading the version of navigation to 2.3.5
                      
                          def nav_version = "2.3.5"
                      
                      Caused by: java.lang.NoClassDefFoundError: com/android/build/api/extension/AndroidComponentsExtension
                          at dagger.hilt.android.plugin.HiltGradlePlugin.configureBytecodeTransformASM(HiltGradlePlugin.kt:257)
                      
                      org.gradle.api.GradleScriptException: A problem occurred evaluating project ':app'.
                          at org.gradle.groovy.scripts.internal.DefaultScriptRunnerFactory$ScriptRunnerImpl.run(DefaultScriptRunnerFactory.java:93)
                          at org.gradle.configuration.DefaultScriptPluginFactory$ScriptPluginImpl.lambda$apply$0(DefaultScriptPluginFactory.java:133)
                          at ...
                      Caused by: java.lang.NoClassDefFoundError: com/android/build/api/extension/AndroidComponentsExtension
                          at com.google.firebase.perf.plugin.FirebasePerfClassVisitorFactory.registerForProject(FirebasePerfClassVisitorFactory.java:54)
                          at com.google.firebase.perf.plugin.FirebasePerfPlugin.perform(FirebasePerfPlugin.java:145)
                          at com.google.firebase.perf.plugin.FirebasePerfPlugin.lambda$apply$0(FirebasePerfPlugin.java:107)
                          at org.gradle.api.internal.plugins.DefaultPluginManager$2.execute(DefaultPluginManager.java:258)
                          at ...
                      

                      Unable to find bundled Java version with flutter doctor, after updating Android studio Arctic Fox(2020.3.1) on M1 Apple Silicon

                      copy iconCopydownload iconDownload
                      cd /Applications/Android\ Studio.app/Contents/jre
                      
                      ln -s ../jre jdk
                      
                      ln -s "/Library/Internet Plug-Ins/JavaAppletPlugin.plugin" jdk
                      
                      flutter doctor -v
                      
                      cd /Applications/Android\ Studio.app/Contents/jre
                      ln -s ../jre jdk
                      
                      nano ~/.zshrc
                      
                      export JAVA_HOME="/Applications/Android Studio.app/Contents/jre/jdk/Contents/Home"
                      
                      source ~/.zshrc
                      
                      flutter doctor
                      
                      cd /Applications/Android\ Studio.app/Contents/jre
                      ln -s ../jre jdk
                      
                      nano ~/.zshrc
                      
                      export JAVA_HOME="/Applications/Android Studio.app/Contents/jre/jdk/Contents/Home"
                      
                      source ~/.zshrc
                      
                      flutter doctor
                      
                      cd /Applications/Android\ Studio.app/Contents/jre
                      ln -s ../jre jdk
                      
                      nano ~/.zshrc
                      
                      export JAVA_HOME="/Applications/Android Studio.app/Contents/jre/jdk/Contents/Home"
                      
                      source ~/.zshrc
                      
                      flutter doctor
                      
                      cd /Applications/Android\ Studio.app/Contents/jre
                      ln -s ../jre jdk
                      
                      nano ~/.zshrc
                      
                      export JAVA_HOME="/Applications/Android Studio.app/Contents/jre/jdk/Contents/Home"
                      
                      source ~/.zshrc
                      
                      flutter doctor
                      
                      cd /Applications/Android\ Studio.app/Contents/jre
                      ln -s ../jre jdk
                      
                      nano ~/.zshrc
                      
                      export JAVA_HOME="/Applications/Android Studio.app/Contents/jre/jdk/Contents/Home"
                      
                      source ~/.zshrc
                      
                      flutter doctor
                      
                      cd /Applications/Android\ Studio.app/Contents/jre
                      ln -s ../jre jdk
                      ln -s "/Library/Internet Plug-Ins/JavaAppletPlugin.plugin" jdk
                      
                      cd /Applications/Android\ Studio.app/Contents/jre
                      ln -s -f ../jre jdk
                      ln -s -f "/Library/Internet Plug-Ins/JavaAppletPlugin.plugin" jdk
                      
                      flutter doctor -v
                      

                      android:exported needs to be explicitly specified for &lt;activity&gt;. Apps targeting Android 12 and higher are required to specify

                      copy iconCopydownload iconDownload
                      <receiver android:name="<name_of_the_entry>"
                                      android:exported="false or true"
                                      tools:node="merge" />
                      
                           <activity
                                      android:name="<activity which is giving error>"
                                      android:exported="true"
                                      tools:node="merge" />
                      
                      <activity android:name="name_of_the_activity_inside_library>"
                          android:exported="false|true"
                          tools:node="merge" />
                      
                      debugImplementation "androidx.fragment:fragment-testing:<version>"
                      
                      androidTestImplementation "androidx.fragment:fragment-testing:<version>"
                      
                      debugImplementation "androidx.fragment:fragment-testing:<version>"
                      
                      androidTestImplementation "androidx.fragment:fragment-testing:<version>"
                      
                       android:exported="true"
                      
                      androidTestImplementation "androidx.test.ext:junit:1.1.3"
                      androidTestImplementation "androidx.compose.ui:ui-test-junit4:1.0.4"
                      
                      > java.util.concurrent.ExecutionException: com.android.builder.testing.api.DeviceException: com.android.ddmlib.InstallException: INSTALL_PARSE_FAILED_MANIFEST_MALFORMED: Failed parse during installPackageLI: /data/app/xxxxx.tmp/base.apk (at Binary XML file line #129): YOUR.FULLY.QUALIFIED.NAME.FAILING.ACTIVITY: Targeting S+ (version 31 and above) requires that an explicit value for android:exported be defined when intent filters are present
                      
                      <activity android:name="androidx.test.core.app.InstrumentationActivityInvoker$BootstrapActivity"
                      android:exported="true"
                      tools:node="merge"/>
                      
                      <activity android:name="androidx.test.core.app.InstrumentationActivityInvoker$EmptyActivity"
                      android:exported="true"
                      tools:node="merge"/>
                      
                      <activity android:name="androidx.test.core.app.InstrumentationActivityInvoker$EmptyFloatingActivity"
                      android:exported="true"
                      tools:node="merge"/>
                      
                       <activity
                              android:name="com.test.activity.SplashActivity"
                              android:clearTaskOnLaunch="true"
                              android:label="@string/app_name"
                              android:launchMode="singleTop"
                              android:noHistory="true"
                              android:screenOrientation="portrait"
                              android:theme="@style/AppTheme.NoActionBar"
                              android:exported="true">
                      
                         <receiver
                              android:name="com.test.receiver.ShareReceiver"
                              android:exported="true">
                              <intent-filter>
                                  <action android:name="com.test.fcm.android.action.broadcast" />
                              </intent-filter>
                          </receiver>
                      
                         <service
                              android:name="com.google.android.gms.tagmanager.InstallReferrerService"
                              android:exported="true" />
                      
                      testImplementation 'junit:junit:4.13.2' 
                      androidTestImplementation 'androidx.test:runner:1.4.0'
                      androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
                      implementation 'com.razorpay:checkout:1.6.15'
                      
                       <activity
                              android:name="com.test.activity.SplashActivity"
                              android:clearTaskOnLaunch="true"
                              android:label="@string/app_name"
                              android:launchMode="singleTop"
                              android:noHistory="true"
                              android:screenOrientation="portrait"
                              android:theme="@style/AppTheme.NoActionBar"
                              android:exported="true">
                      
                         <receiver
                              android:name="com.test.receiver.ShareReceiver"
                              android:exported="true">
                              <intent-filter>
                                  <action android:name="com.test.fcm.android.action.broadcast" />
                              </intent-filter>
                          </receiver>
                      
                         <service
                              android:name="com.google.android.gms.tagmanager.InstallReferrerService"
                              android:exported="true" />
                      
                      testImplementation 'junit:junit:4.13.2' 
                      androidTestImplementation 'androidx.test:runner:1.4.0'
                      androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
                      implementation 'com.razorpay:checkout:1.6.15'
                      
                       <activity
                              android:name="com.test.activity.SplashActivity"
                              android:clearTaskOnLaunch="true"
                              android:label="@string/app_name"
                              android:launchMode="singleTop"
                              android:noHistory="true"
                              android:screenOrientation="portrait"
                              android:theme="@style/AppTheme.NoActionBar"
                              android:exported="true">
                      
                         <receiver
                              android:name="com.test.receiver.ShareReceiver"
                              android:exported="true">
                              <intent-filter>
                                  <action android:name="com.test.fcm.android.action.broadcast" />
                              </intent-filter>
                          </receiver>
                      
                         <service
                              android:name="com.google.android.gms.tagmanager.InstallReferrerService"
                              android:exported="true" />
                      
                      testImplementation 'junit:junit:4.13.2' 
                      androidTestImplementation 'androidx.test:runner:1.4.0'
                      androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
                      implementation 'com.razorpay:checkout:1.6.15'
                      
                      "com.google.dagger:hilt-android:2.38.1"
                      "com.google.dagger:hilt-android-gradle-plugin:2.38.1"
                      "com.google.dagger:hilt-android-compiler:2.38.1"
                      "com.google.dagger:hilt-android-testing:2.38.1"
                      
                      "com.google.dagger:hilt-android:2.40.5"
                      "com.google.dagger:hilt-android-gradle-plugin:2.40.5"
                      "com.google.dagger:hilt-android-compiler:2.40.5"
                      "com.google.dagger:hilt-android-testing:2.40.5" 
                      
                      "com.google.dagger:hilt-android:2.38.1"
                      "com.google.dagger:hilt-android-gradle-plugin:2.38.1"
                      "com.google.dagger:hilt-android-compiler:2.38.1"
                      "com.google.dagger:hilt-android-testing:2.38.1"
                      
                      "com.google.dagger:hilt-android:2.40.5"
                      "com.google.dagger:hilt-android-gradle-plugin:2.40.5"
                      "com.google.dagger:hilt-android-compiler:2.40.5"
                      "com.google.dagger:hilt-android-testing:2.40.5" 
                      
                      <receiver
                          android:name="com.razorpay.RzpTokenReceiver"
                          android:exported="false">
                          <intent-filter>
                              <action android:name="rzp.device_token.share" />
                          </intent-filter>
                      </receiver>
                      
                      <activity
                          android:name="com.razorpay.CheckoutActivity"
                          android:configChanges="keyboard|keyboardHidden|orientation|screenSize"
                          android:exported="true"
                          android:theme="@style/CheckoutTheme">
                          <intent-filter>
                              <action android:name="android.intent.action.MAIN" />
                              <data
                                  android:host="rzp.io"
                                  android:scheme="io.rzp" />
                          </intent-filter>
                      </activity>
                      
                      android:exported="true" <!-- or false as required -->
                      
                      <activity
                           android:name=".MainActivity"
                           android:exported="true" <** add this line on AndroidManifest.xml**
                           android:launchMode="singleTop"
                           android:theme="@style/LaunchTheme"
                       </activity>
                      

                      Targeting S+ (version 31 and above) requires that one of FLAG_IMMUTABLE or FLAG_MUTABLE be specified when creating a PendingIntent, On AlarmPingSender

                      copy iconCopydownload iconDownload
                      implementation 'androidx.work:work-runtime-ktx:2.7.0-beta01'
                      
                      dependencies {
                        // For Java
                        implementation 'androidx.work:work-runtime:2.7.1' 
                      
                        // For Kotlin
                        implementation 'androidx.work:work-runtime-ktx:2.7.1'
                      }
                      
                      <uses-permission android:name="android.permission.SCHEDULE_EXACT_ALARM"/>
                      
                      implementation 'com.google.firebase:firebase-messaging:20.0.0'
                      
                      implementation 'com.google.firebase:firebase-messaging:23.0.0'
                      
                      implementation 'com.google.firebase:firebase-messaging:20.0.0'
                      
                      implementation 'com.google.firebase:firebase-messaging:23.0.0'
                      
                      dependencies {
                          // For Java
                          implementation 'androidx.work:work-runtime:2.7.1' 
                          // For Kotlin
                          implementation 'androidx.work:work-runtime-ktx:2.7.1'
                          implementation 'com.google.firebase:firebase-messaging:23.0.0'
                          ...
                      }
                      
                      PendingIntent pendingIntent = PendingIntent.getActivity(this, alarmID, notificationIntent, PendingIntent.FLAG_IMMUTABLE);
                      
                      dependencies {
                          // For Java
                          implementation 'androidx.work:work-runtime:2.7.1' 
                          // For Kotlin
                          implementation 'androidx.work:work-runtime-ktx:2.7.1'
                          implementation 'com.google.firebase:firebase-messaging:23.0.0'
                          ...
                      }
                      
                      PendingIntent pendingIntent = PendingIntent.getActivity(this, alarmID, notificationIntent, PendingIntent.FLAG_IMMUTABLE);
                      

                      uploaded an APK which has an activity,activity alias,service or broadcast receiver with intentfilter, but without 'android : exported' property set

                      copy iconCopydownload iconDownload
                      <service android:name="com.example.app.backgroundService"
                               android:exported="false">
                          <intent-filter>
                              <action android:name="com.example.app.START_BACKGROUND" />
                          </intent-filter>
                      </service>
                      
                       <receiver android:name="com.example.app.serives.SilentPushReceiver"
                                  android:exported="false">
                                  <intent-filter>
                                      <!-- Receive silent push notifications. -->
                                      <action 
                                      android:name="uz.usoft.kidya.action.ymp.SILENT_PUSH_RECEIVE"/>
                                  </intent-filter>
                      </receiver>
                      
                      <activity android:name="com.example.app.SplashScreenActivity"
                                  android:exported="true">
                                  <intent-filter>
                                      <action android:name="android.intent.action.MAIN" />
                      
                                      <category android:name="android.intent.category.LAUNCHER" />
                                  </intent-filter>
                              </activity>
                      
                      <activity
                                  android:name="com.example.app.MainActivity"
                                  android:exported="false"/>
                      
                      -keepresourcexmlattributenames manifest/**
                      
                      <service android:name="com.example.app.backgroundService"
                           android:exported="false">
                      <intent-filter>
                          <action android:name="com.example.app.START_BACKGROUND" />
                      </intent-filter>
                      
                      <?xml version="1.0" encoding="utf-8"?>
                      <manifest xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" package="com.unity3d.player" android:installLocation="preferExternal" tools:ignore="MissingLeanbackSupport">
                        <uses-permission android:name="android.permission.INTERNET" />
                        <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
                        <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
                        <uses-permission android:name="com.google.android.finsky.permission.BIND_GET_INSTALL_REFERRER_SERVICE" />
                        <uses-feature android:glEsVersion="0x00020000" />
                        <application android:name="androidx.multidex.MultiDexApplication" android:fullBackupContent="false" android:allowBackup="false" android:theme="@android:style/Theme.NoTitleBar" tools:ignore="GoogleAppIndexingWarning,MissingTvBanner" tools:replace="fullBackupContent,allowBackup">
                          <!-- UNITY -->
                          <activity android:name="com.unity3d.player.UnityPlayerActivity" android:label="@string/app_name" android:screenOrientation="fullSensor" android:launchMode="singleTask" android:configChanges="mcc|mnc|locale|touchscreen|keyboard|keyboardHidden|navigation|orientation|screenLayout|uiMode|screenSize|smallestScreenSize|fontScale|layoutDirection|density" android:resizeableActivity="false" android:hardwareAccelerated="false" android:exported="true">
                            <intent-filter>
                              <action android:name="android.intent.action.MAIN" />
                              <category android:name="android.intent.category.LAUNCHER" />
                              <category android:name="android.intent.category.LEANBACK_LAUNCHER" />
                            </intent-filter>
                            <meta-data android:name="unityplayer.UnityActivity" android:value="true" />
                            <meta-data android:name="unityplayer.ForwardNativeEventsToDalvik" android:value="false" />
                            <meta-data android:name="com.google.android.gms.version" android:value="@integer/google_play_services_version" />
                            <meta-data android:name="android.notch_support" android:value="true" />
                          </activity>
                          <!-- FULLSCREEN FIX -->
                          <meta-data android:name="android.max_aspect" android:value="2.16" />
                          <!-- 3rdParty MANIFEST -->
                          <activity android:name="com.facebook.unity.FBUnityLoginActivity" android:exported="true" android:configChanges="fontScale|keyboard|keyboardHidden|locale|mnc|mcc|navigation|orientation|screenLayout|screenSize|smallestScreenSize|uiMode|touchscreen" android:theme="@android:style/Theme.Translucent.NoTitleBar.Fullscreen" />
                          <activity android:name="com.facebook.unity.FBUnityDialogsActivity" android:exported="true" android:configChanges="fontScale|keyboard|keyboardHidden|locale|mnc|mcc|navigation|orientation|screenLayout|screenSize|smallestScreenSize|uiMode|touchscreen" android:theme="@android:style/Theme.Translucent.NoTitleBar.Fullscreen" />
                          <activity android:name="com.facebook.unity.FBUnityGamingServicesFriendFinderActivity" android:exported="true" android:configChanges="fontScale|keyboard|keyboardHidden|locale|mnc|mcc|navigation|orientation|screenLayout|screenSize|smallestScreenSize|uiMode|touchscreen" android:theme="@android:style/Theme.Translucent.NoTitleBar.Fullscreen" />
                          <activity android:name="com.facebook.unity.FBUnityAppLinkActivity" android:exported="true" />
                          <activity android:name="com.facebook.unity.FBUnityDeepLinkingActivity" android:exported="true" />
                          <activity android:name="com.facebook.unity.FBUnityGameRequestActivity" android:exported="true"/>
                          <activity android:name="com.facebook.unity.FBUnityCreateGameGroupActivity" android:exported="true"/>
                          <activity android:name="com.facebook.unity.FBUnityJoinGameGroupActivity" android:exported="true"/>
                          <meta-data android:name="com.facebook.sdk.ApplicationId" android:value="fb901505887229125" />
                          <meta-data android:name="com.facebook.sdk.AutoLogAppEventsEnabled" android:value="true" />
                          <meta-data android:name="com.facebook.sdk.AdvertiserIDCollectionEnabled" android:value="true" />
                          <provider android:name="com.facebook.FacebookContentProvider" android:authorities="com.facebook.app.FacebookContentProvider901505887229125" android:exported="true" />
                          <meta-data android:name="unity.splash-mode" android:value="0" />
                          <meta-data android:name="unity.splash-enable" android:value="True" />
                          <meta-data android:name="unity.allow-resizable-window" android:value="False" />
                          <meta-data android:name="notch.config" android:value="portrait|landscape" />
                          <meta-data android:name="unity.build-id" android:value="31d4e179-c52c-49d7-a4f5-da548e453521" />
                          <receiver android:name="com.unity.androidnotifications.UnityNotificationManager" android:exported="true" />
                          <receiver android:name="com.unity.androidnotifications.UnityNotificationRestartOnBootReceiver" android:exported="true" android:enabled="false">
                            <intent-filter>
                              <action android:name="android.intent.action.BOOT_COMPLETED" />
                            </intent-filter>
                          </receiver>
                        </application>
                        <uses-feature android:name="android.hardware.vulkan.version" android:required="false" />
                        <uses-feature android:name="android.hardware.touchscreen" android:required="false" />
                        <uses-feature android:name="android.hardware.touchscreen.multitouch" android:required="false" />
                        <uses-feature android:name="android.hardware.touchscreen.multitouch.distinct" android:required="false" />
                      </manifest>
                      
                       <activity
                              android:name=".MainActivity"
                              android:launchMode="singleTop"
                              android:theme="@style/LaunchTheme"
                              android:configChanges="orientation|keyboardHidden|keyboard|screenSize|smallestScreenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
                              android:hardwareAccelerated="true"
                              android:windowSoftInputMode="adjustResize"
                              android:exported="true"> //added this line
                             
                              <meta-data
                                android:name="io.flutter.embedding.android.NormalTheme"
                                android:resource="@style/NormalTheme"
                                />
                             
                              <meta-data
                                android:name="io.flutter.embedding.android.SplashScreenDrawable"
                                android:resource="@drawable/launch_background"
                                />
                              <intent-filter>
                                  <action android:name="android.intent.action.MAIN"/>
                                  <category android:name="android.intent.category.LAUNCHER"/>
                              </intent-filter>
                          </activity>
                      
                      1. Enter the following commands on terminal
                         flutter pub upgrade --major-versions
                         flutter clean
                         flutter build appbundle
                      
                      2. Add android:exported="true" on AndroidManifest.xml
                         <activity
                              android:name=".MainActivity"
                              android:exported="true"
                              ...
                         </activity>
                      

                      Log4j vulnerability - Is Log4j 1.2.17 vulnerable (was unable to find any JNDI code in source)?

                      copy iconCopydownload iconDownload
                      zip -d log4j-1.2.16.jar org/apache/log4j/net/JMSAppender.class
                      zip -d log4j-1.2.16.jar org/apache/log4j/net/SocketServer.class
                      
                      #!/bin/bash
                      
                      DIR=$1
                      APPLY=$2
                      
                      # Classes to be searched for/removed
                      CLASSES="org/apache/log4j/net/SimpleSocketServer.class
                      org/apache/log4j/net/SocketServer.class
                      org/apache/log4j/net/JMSAppender.class"
                      
                      
                      PROGNAME=`basename $0`
                      PROGPATH=`echo $0 | sed -e 's,[\\/][^\\/][^\\/]*$,,'`
                      
                      usage () {
                          echo >&2 Usage: ${PROGNAME} DIR [APPLY]
                          echo >&2        Where DIR is the starting directory for find
                          echo >&2        and   APPLY = "Y" - to perform purification
                          exit 1
                      }
                      
                      # Force upper case on Apply
                      APPLY=$(echo "${APPLY}" | tr '[:lower:]' '[:upper:]')
                      
                      # Default Apply to N
                      if [ "$APPLY" == "" ] ; then
                         APPLY="N"
                      fi
                      
                      # Check parameters
                      if [ "$DIR" == "" ] ; then
                         usage
                      fi
                      echo $APPLY | grep -q -i -e '^Y$' -e '^N$' || usage
                      
                      # Search for log4j jar files - for class file removal
                      FILES=$(find $DIR -name *log4j*jar)
                      for f in $FILES
                      do
                         echo "Checking Jar [$f]"
                      
                         for jf in $CLASSES
                         do
                            unzip -v $f | grep -e "$jf"
                            if [ "$APPLY" = "Y" ]
                            then
                               echo "Deleting $jf from $f"
                               zip -d $f $jf
                            fi
                         done
                      done
                      
                      # Search for Log4j properties files - for read-only setting
                      PFILES=$(find $DIR -name *log4j*properties)
                      for f in $PFILES
                      do
                         echo "Checking permissions [$f]"
                      
                         if [ "$APPLY" = "Y" ]
                         then
                            echo "Changing permissons on $f"
                            chmod 444 $f
                         fi
                      
                         ls -l $f
                      done
                      

                      Why do I get an ambiguity error in this code?

                      copy iconCopydownload iconDownload
                      static void f(int x) {}
                      static void f(float x) {}
                      
                      static void f(int x, B a) {}
                      static void f(float x, A a) {}
                      
                      static void f(int x, A a) {}
                      static void f(float x, A a) {}
                      
                      static void f(int x) {}
                      static void f(float x) {}
                      
                      static void f(int x, B a) {}
                      static void f(float x, A a) {}
                      
                      static void f(int x, A a) {}
                      static void f(float x, A a) {}
                      
                      static void f(int x) {}
                      static void f(float x) {}
                      
                      static void f(int x, B a) {}
                      static void f(float x, A a) {}
                      
                      static void f(int x, A a) {}
                      static void f(float x, A a) {}
                      
                      fFloat(float f){}
                      int intValue = 221;
                      fFloat(intValue); // inside f, intValue is treated as 221.0
                      
                      fInt(int i){}
                      float floatVal = 221.221;
                      fInt(floatVal); // what should compiler do with remaining .221 part?
                      
                      class A {
                      public void f() {}
                      }
                      
                      class B extends A {
                      public void g() {}
                      }
                      
                      fA(A a){}
                      B bInst = new B();
                      fA(bInst); // you can refer only to f() method, not g()
                      
                      fB(B b){}
                      A aInst = new A();
                      fB(aInst); // you cannot do this, as subclass can have some additional
                      // stuff, that superclass does not have
                      
                      //but even
                      A aInstBImpl = new B();
                      fB(aInstBImpl); // will not work without explicit casting as it is
                      // kind of A instance with B implementation - here polymorphism comes into action
                      
                      fFloat(float f){}
                      int intValue = 221;
                      fFloat(intValue); // inside f, intValue is treated as 221.0
                      
                      fInt(int i){}
                      float floatVal = 221.221;
                      fInt(floatVal); // what should compiler do with remaining .221 part?
                      
                      class A {
                      public void f() {}
                      }
                      
                      class B extends A {
                      public void g() {}
                      }
                      
                      fA(A a){}
                      B bInst = new B();
                      fA(bInst); // you can refer only to f() method, not g()
                      
                      fB(B b){}
                      A aInst = new A();
                      fB(aInst); // you cannot do this, as subclass can have some additional
                      // stuff, that superclass does not have
                      
                      //but even
                      A aInstBImpl = new B();
                      fB(aInstBImpl); // will not work without explicit casting as it is
                      // kind of A instance with B implementation - here polymorphism comes into action
                      

                      Community Discussions

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                      • android:exported needs to be explicitly specified for &lt;activity&gt;. Apps targeting Android 12 and higher are required to specify
                      • Targeting S+ (version 31 and above) requires that one of FLAG_IMMUTABLE or FLAG_MUTABLE be specified when creating a PendingIntent, On AlarmPingSender
                      • uploaded an APK which has an activity,activity alias,service or broadcast receiver with intentfilter, but without 'android : exported' property set
                      • Log4j vulnerability - Is Log4j 1.2.17 vulnerable (was unable to find any JNDI code in source)?
                      Trending Discussions on Java

                      QUESTION

                      How do purely functional languages handle index-based algorithms?

                      Asked 2022-Apr-05 at 12:51

                      I have been trying to learn about functional programming, but I still struggle with thinking like a functional programmer. One such hangup is how one would implement index-heavy operations which rely strongly on loops/order-of-execution.

                      For example, consider the following Java code:

                      public class Main {
                          public static void main(String[] args) {
                              List<Integer> nums = Arrays.asList(1,2,3,4,5,6,7,8,9);
                              System.out.println("Nums:\t"+ nums);
                              System.out.println("Prefix:\t"+prefixList(nums));
                          }
                        
                          private static List<Integer> prefixList(List<Integer> nums){
                            List<Integer> prefix = new ArrayList<>(nums);
                            for(int i = 1; i < prefix.size(); ++i)
                              prefix.set(i, prefix.get(i) + prefix.get(i-1));
                            return prefix;
                          }
                      }
                      /*
                      System.out: 
                      Nums:   [1, 2, 3, 4, 5, 6, 7, 8, 9]
                      Prefix: [1, 3, 6, 10, 15, 21, 28, 36, 45]
                      */
                      

                      Here, in the prefixList function, the nums list is first cloned, but then there is the iterative operation performed on it, where the value on index i relies on index i-1 (i.e. order of execution is required). Then this value is returned.

                      What would this look like in a functional language (Haskell, Lisp, etc.)? I have been learning about monads and think they may be relevant here, but my understanding is still not great.

                      ANSWER

                      Answered 2022-Mar-07 at 21:17

                      This is not an index-heavy operation, in fact you can do this with a one-liner with scanl1 :: (a -> a -> a) -> [a] -> [a]:

                      prefixList = scanl1 (+)
                      

                      indeed, for the list of Nums, we get:

                      Prelude> prefixList [1 .. 9]
                      [1,3,6,10,15,21,28,36,45]
                      

                      scanl1 takes the first item of the original list as initial value for the accumulator, and yields that. Then each time it takes the accumulator and the next item of the given list, and sums these up as new accumulator, and yields the new accumulator value.

                      Often one does not need indexing, but enumerating over the list is sufficient. Imperative programming languages often work with for loops with indexes, but in many cases these can be replaced by foreach loops that thus do not take the index into account. In Haskell this also often helps to make algorithms more lazy.

                      If you really need random access lookups, you can work with data structures such as defined in the array and vector packages.

                      Source https://stackoverflow.com/questions/71387267

                      Community Discussions, Code Snippets contain sources that include Stack Exchange Network

                      Vulnerabilities

                      No vulnerabilities reported

                      Install Java

                      You can download it from GitHub.
                      You can use Java like any standard Java library. Please include the the jar files in your classpath. You can also use any IDE and you can run and debug the Java component as you would do with any other Java program. Best practice is to use a build tool that supports dependency management such as Maven or Gradle. For Maven installation, please refer maven.apache.org. For Gradle installation, please refer gradle.org .

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