JPanel fills all JFrame space

问题:

I have write this code for displaying some set of colors from panel:

import java.util.ArrayList;
import java.util.List;

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

public class Palette {

    public static void main(String[] args) {
        JFrame frame = new JFrame("Panel");

        palette.add(new Color(255, 0, 0));
        palette.add(new Color(0, 255, 0));
        palette.add(new Color(0, 0, 255));

        int width = 100;
        int height = 250;
        int x = 0;
        for (Color color : palette) {
            JPanel panel = new JPanel();

            panel.setSize(width, height);
            panel.setLocation(x, 750);
            panel.setBackground(new java.awt.Color(color.getColor()));

            frame.add(panel);

            x+=width;
        }
        frame.pack();

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(1000, 1000);
        frame.setVisible(true);
    }

}

Two first panels in the right place and with right dimensions. But the last one fills all frame in blue color. What's wrong?

回答1:

You have to use the appropriate Layout Manager. A JFrame by default has a BorderLayout.

Check out this tutorial for LayoutManagers:

http://docs.oracle.com/javase/tutorial/uiswing/layout/visual.html

回答2:

1. You haven't set a LayoutManager on the frame. I'm not sure what the default LayoutManager is in Swing, but it's likely the LayoutManager is just stacking the components in Z order when you call pack().
2. You should use setPreferredSize(Dimension d), not setSize(int x, int y) - from what I recall the LayoutManagers prefer this.