a curious problem about canvas

[alan fisher]

I add two canvas into a panel, as for these tow canvas, I set different background,but when the program runs,it shows only one canvas,why?
The test source code as follows:


import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.*;
import javax.swing.*;


public class Test
{
public static void main(String[] args)
{
JFrame frame = new MainFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.show();
}
}

class MainFrame extends JFrame {
public MainFrame()
{
setSize(300,300);
setTitle("BounceThread");
Container contentPane = getContentPane();
JPanel jPanel2 = new JPanel();
contentPane.add(jPanel2);

jPanel2.setLayout(new BorderLayout());
Canvas nodeCanvas=new Canvas();
Canvas topoCanvas=new Canvas();
nodeCanvas.setSize(jPanel2.getWidth(),(int)0.6*jPanel2.getHeight());
nodeCanvas.setBackground(new Color(255,0,255));
topoCanvas.setSize(jPanel2.getWidth(),(int)0.4*jPanel2.getHeight());
topoCanvas.setForeground(new Color(0,255,255));
jPanel2.add(nodeCanvas,BorderLayout.CENTER);
jPanel2.add(topoCanvas,BorderLayout.SOUTH);
}
}

[Dirk Schreckmann]

Moving this to the Swing / JFC / AWT forum...

[Craig Wood]

Swing likes the setPreferredSize method. Also, in Swing we use either JComponent or JPanel instead of Canvas. It is recommended not to mix heavyweight AWT components with lightweight Swing components.

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.*;
import javax.swing.*;
 
public class TestRx
{
    public static void main(String[] args)
    {
        JFrame frame = new MainFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.show();
    }
}
 
class MainFrame extends JFrame {
    public MainFrame()
    {
        setSize(300,300);
        setTitle("BounceThread");
        Container contentPane = getContentPane();
        JPanel jPanel2 = new JPanel();
        contentPane.add(jPanel2);
        jPanel2.setPreferredSize(getSize());
 
        jPanel2.setLayout(new BorderLayout());
        JPanel nodeCanvas = new JPanel();
        JPanel topoCanvas = new JPanel();
        nodeCanvas.setPreferredSize(new Dimension(jPanel2.getPreferredSize().width,
                                    (int)(0.6*jPanel2.getPreferredSize().height)));
        nodeCanvas.setBackground(new Color(255,0,255));
        topoCanvas.setPreferredSize(new Dimension(jPanel2.getPreferredSize().width,
                                    (int)(0.4*jPanel2.getPreferredSize().height)));
        topoCanvas.setForeground(new Color(0,255,255));
        jPanel2.add(nodeCanvas,BorderLayout.CENTER);
        jPanel2.add(topoCanvas,BorderLayout.SOUTH);
        System.out.println("nodeCanvas " + nodeCanvas.getPreferredSize() + "\n" +
                           "topoCanvas " + topoCanvas.getPreferredSize() + "\n" +
                           "jPanel2 = " + jPanel2.getPreferredSize());
    }
}