CODEWITHSUNDEEP
javaswingborder-layout
SmithNineSix
SmithNineSix

Reputation: 69

Existence of JPanel when reassigned in layout

I wrote up this quick example to see what happens when the value of an area in a BorderLayout is superimposed with new content (or replaced?).

import java.awt.*;
import javax.swing.*;

public class Test {

  public static void main(String[] args) {

    JPanel add1 = new JPanel();
    add1.setBackground(Color.RED);

    JPanel add2 = new JPanel();
    add2.setBackground(Color.DARK_GRAY);

    JPanel pane = new JPanel();
    pane.setLayout(new BorderLayout());
    pane.add(add1, BorderLayout.NORTH);
    pane.add(add2, BorderLayout.NORTH);

    JFrame main = new JFrame();
    main.setContentPane(pane);
    main.setPreferredSize(new Dimension(300,300));
    main.setLocation(200,300);
    main.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    main.setResizable(false);
    main.setVisible(true);
    main.pack();
  }
}

What I was wondering is what happens to add1 when BorderLayout.NORTH is reassigned? Does the garbage collector handle it?

I would assume not as there is still a reference to add1 inside the class Test, however I'm not sure if it is still considered part of the JFrame. If I'm going to be replacing BorderLayout.NORTH, will I need to set add1 to null? I guess what I'm asking is if a layout reference is replaced, is the new value superimposed into that position, or is the old value replaced completely and thus no longer part of the JFrame.

Upvotes: 0

Views: 33

Answers (1)

Hovercraft Full Of Eels
Hovercraft Full Of Eels

Reputation: 285405

As per most similar questions, the Java API holds the answers. Here the BorderLayout API specifically states (highlighting mine):

A border layout lays out a container, arranging and resizing its components to fit in five regions: north, south, east, west, and center. Each region may contain no more than one component, and is identified by a corresponding constant: NORTH, SOUTH, EAST, WEST, and CENTER.

So by adding a new component to the NORTH section, you displace the old one, and it is no longer part of the GUI.

Upvotes: 4

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