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This looks like a perfect case for reduce():

If in a map you want to store multiple values associated with the same key, the value type must be suitable for that. A struct isn't, but a slice is a perfect choice.

So change your value type to []A:

You are using TextView without setting test layout as content view. Try to set content view first setContentView(R.layout.test) then use view as per your needs.

Try this:

Actually your panel is centered in the frame, but what it draws isn't.

You should make use of the width and the height of the JPanel to center the drawing .

Also put your sizes and numbers into variables, it is less error-prone when you use them several times in your code .

Finally as @MadProgrammer said in the comments :

Don't forget to call super.paintComponent before you doing any custom painting, strange things will start doing wrong if you don't. Also paintComponent doesn't need to be public, no one should ever call it directly