创建jpanels后更改其颜色

Question

I am trying to make a GUI maze game, where as the computer tries to solve the maze, it changes the colors of the point in the maze it is on. The maze is made up of a JFrame with a JPanel (GridLayout). In the grid is the JPanels that I need to change their colors. I'm not sure how to even access them after I create them.

My code:

public Maze(int length) {

    JFrame frame = new JFrame();
    JPanel panel = new JPanel(new GridLayout(length, length, 5,5));
    panel.setPreferredSize(new Dimension(500, 500));

    for (int i = 0; i < length; i++) {
        for (int j = 0; j < length; j++) {               
            JPanel p2 = new JPanel();
            p2.setBackground(Color.red);           

            panel.add(p2);
        }
    }

    frame.setDefaultCloseOperation(3);
    frame.setTitle("Maze Game");
    frame.setContentPane(panel);
    frame.pack();
    frame.setVisible(true);
}

Is there a way to change the color of p2 in a different method? Or is there a better way to do it?

Answer 1

If your have the referee of JFrame then you can do it in this way.

    int count = 0;
    for (Component comp : frame.getContentPane().getComponents()) {
        System.out.println(comp.getBackground());
        if (count == 6) {
            comp.setBackground(Color.GREEN);
        }
        count++;
    }

Here 6 represent 2nd row and 3rd column as in the same order the JPanel are added in JFrame .

---

Complete Sample Code [EDITED]

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.GridLayout;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;

public class Maze {
    private JFrame frame = null;

    public Maze(int length) {

        frame = new JFrame();

        JPanel panel = new JPanel(new GridLayout(length, length, 5, 5)) {
            private static final long serialVersionUID = 1L;

            @Override
            public Dimension getPreferredSize() {
                return new Dimension(500, 500);
            }
        };

        for (int i = 0; i < length; i++) {
            for (int j = 0; j < length; j++) {
                JPanel p2 = new JPanel();
                p2.setBackground(Color.red);

                panel.add(p2);
            }
        }

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setTitle("Maze Game");
        frame.setContentPane(panel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public void setPanelColor(int index) {
        frame.getContentPane().getComponents()[index].setBackground(Color.GREEN);
    }

    public static void main(String[] a) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                try {                        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (Exception ex) {
                }
                Maze maze = new Maze(4);
                maze.setPanelColor(6);
            }
        });
    }
}

Edits:

1. EventQueue.invokeLater()

   All GUI related things in java should always go through a single thread. The thread is our legendary AWT-EventQueue . Hence all GUI related actions should necessarily go through the AWT Event thread. If not so you may end up in a deadlock .

   Read more Should we use EventQueue.invokeLater for any GUI update in a Java desktop application?

2. UIManager.setLookAndFeel()

   UIManager manages the current look and feel, the set of available look and feels.

   Read more How to Set the Look and Feel

3. JComponent#getPreferredSize()

   Read more Should I avoid the use of set(Preferred|Maximum|Minimum)Size methods in Java Swing?