Singleton | javascript单例模式及登录窗口实例
kandi X-RAY | Singleton Summary
kandi X-RAY | Singleton Summary
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Lines of Code : 27License : Non-SPDX
Copypublic static ThreadSafeDoubleCheckLocking getInstance() {
// local variable increases performance by 25 percent
// Joshua Bloch "Effective Java, Second Edition", p. 283-284
var result = instance;
// Check if singleton instance is in def newton_raphson(f, x0=0, maxiter=100, step=0.0001, maxerror=1e-6, logsteps=False):
a = x0 # set the initial guess
steps = [a]
error = abs(f(a))
f1 = lambda x: calc_derivative(f, x, h=step) # noqa: E731 Derivative of f(x)
fo public static synchronized Db getInstance() {
if (instance == null) {
Db newInstance = new Db();
newInstance.userName2User = new HashMap<>();
newInstance.user2Account = new HashMap<>();
newInstance.itemName2Pro Community Discussions
Trending Discussions on Singleton
QUESTION
So I am relatively new to programming, and I have been working on this task app, where I want to save the data such as task name and more, given by the user. I am trying to accomplish this using Room. Now, initially, when I tried to do it, the app would crash since I was doing everything on the main thread probably. So, after a little research, I came to AsyncTask, but that is outdated. Now finally I have come across the Executer. I created a class for it, but I am a little unsure as to how I can implement it in my app. This is what I did :
Entity Class :
...ANSWER
Answered 2021-Jun-14 at 12:03First make a Repository class and make an instance of your DAO
QUESTION
I have written the following class in Typescript:
...ANSWER
Answered 2021-Jun-15 at 07:47SaxonJS.getResource() is asynchronous and returns a Promise; I think you have supplied this Promise to SaxonJS.XPath.Evaluate(), which is treating it as a general Javascript object.
You need something like
QUESTION
Given the list [1, 2, 3, 4], display the last element. I am using only one parameter and using recursion.
This is what I tried. But the output is always true.
ANSWER
Answered 2021-May-25 at 09:20I think you over thought this.
The predicate lastElement(Stack). will match on everything. You just want the last element of the list.
Try this:
QUESTION
public class FileStorage
{
private static FileStorage _instance;
public static FileStorage instance
{
get
{
return (_instance != null) ? _instance : _instance = new FileStorage();
}
}
//public string GetAddress...
}
ANSWER
Answered 2021-Jun-14 at 15:30Yes, this would work as you intended. However, even if you are working with a single-threaded application, keep in mind that this method is not thread-safe.
Still, to avoid going on a bug hunt when you need to use threads in your app, it is usually better to ensure thread safety precautionarily.
For example:
QUESTION
I am experimenting with loading views from a database, and as suggested in the article one might want to add some caching to prevent hitting the database every time.
ConfigureServices:
ANSWER
Answered 2021-Jun-14 at 14:15Use DI services to configure MvcRazorRuntimeCompilationOptions directly
Assuming a target provider like
QUESTION
Dears, I have a jersey - spring api deployed on apache tomcat 9.0.46. (Jersey to handle restful services JAX-RS and Spring to handle all my beans{controllers, DAO, SessionFactory, JPA etc...}). Everything works fine on tomcat 9 on windows... When deploying the exact same war in ubuntu tomcat 9.0.46, the ContextLoader is getting triggered 3 times and I have all my singletons instantiated 3 times. I'm deploying the api on tomcat ports 80 and 443 (https - godady certificate). once I start tomcat the war is deployed and ports 80 and 443 get started (netstat -tulnp | grep java) and I see in log all singletons instantiated. (pool-2) Applicationcontext class my custom spring @Configuration class and it is getting triggered and DB is accessed without any issues
...ANSWER
Answered 2021-Jun-14 at 12:43I have managed to figure out the problem. The issue was related to tomcat configuration in /conf/server.xml. Multiple Hosts will trigger the context loader to be triggered for each. I was keeping the default appBase to webapps for all host thus triggering the ContextLoader of each my war for each host. Another reason the ContextLoader will triggered multiple times as well is defining the option inside unless you need to load something external to your war. I recommend reading specs: https://tomcat.apache.org/tomcat-4.1-doc/config/host.html
QUESTION
dispatcher-servlet.xml
...ANSWER
Answered 2021-Jun-14 at 02:53This issue is solved after correcting up my code
QUESTION
In a singleton class I am trying the following code with 3 URLs stored in a dictionary:
...ANSWER
Answered 2021-Jun-13 at 10:59urls is actually of type [String: URL?]. Note that the value type is optional, because URL.init(string:) is failable.
When you try to get a value from this dictionary, you get a URL??. The guard only unwraps one layer of the optional.
One way to unwrap a nested optional (no matter how many layers), is to use as?:
QUESTION
I have looked through various examples on how to do this and I have got to this stage. My data import is copied into the array list but I am not seeing the data where I thought it would be.
When I use a 2D array it displays the imported data fine, but I want to be able to make changes to the data, hence the array list. I need the data to populate two things, first a Java Table and then I will reuse the data in an export to a spreadsheet. If you can just help me with the conversion of 2D array to a 2D (if this is what I need) ArrayList that would be great.
ANSWER
Answered 2021-Jun-13 at 01:52a) Do the DataImport.dataImport(file_path) only once before loops, no need to read it all the time inside the loop
QUESTION
I have a settings array of config values that don't change and need to use these values in various classes.
...ANSWER
Answered 2021-Jun-05 at 17:51If these values really are fixed, you could have the classes import a trait that holds the settings and also incorporates any common functionality you need.
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