无法添加JFrame和JTextField

Question

Here's part of my simple code where I can move rectangle on a frame. When I try to add button and text field on frame, these components are not visible or I can't see rectangle. I also tried adding them first on JPanel and then adding panel on frame. Components were visible but rectangle wasn't. Any suggestions?

public class Buffer extends JPanel implements KeyListener,ActionListener{
public static JFrame frame;
public static JButton button;
public static JTextField field;
public int x;
public int y;

    public void paintComponent(Graphics g){
    super.paintComponent(g);
    g.setColor(Color.red);
    g.fillRect(x,y,20,20);
}

public static void main(String args[]){
    Buffer z=new Buffer();
    frame=new JFrame();
    button=new JButton();
    field=new JTextField(); 
    frame.setLayout(new BorderLayout());

    button.setPreferredSize(new Dimension(20,20));
    button.setText("XY");
    button.addActionListener(z);

    field.setPreferredSize(new Dimension(100,20));
    field.setEditable(false);

    frame.setSize(500,500);
    frame.setVisible(true);
    frame.setFocusable(true);
    frame.addKeyListener(z);
    frame.setTitle("TEST");
}
@Override
public void keyPressed(KeyEvent e) {
    if(e.getKeyCode()==KeyEvent.VK_RIGHT){
        x=x+10;
        repaint();
    }
    }
    public void actionPerformed(ActionEvent e){
    field.setText("X- "+x+"       Y- "+y);
    frame.requestFocusInWindow();
}
    }
    }

Answer 1

• JFrame by default never to react to KeyEvent , meaning frame.setFocusable(true);

• have to setFocusable(true) for JPanel , then KeyEvents from KeyListener are firing an desired event(s)

---

• don't to use KeyListener for Swing JComponent , use (most scallable, settable) KeyBindings instead ( for example )

• use constant for BorderLayout , only one JComponent can be visible, placed to the one of 5th. areas

Answer 2

To add components to the frame you have to get the Container of the frame then you add the components to the container.

for example a sample program

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

public class Test
{
JFrame f;
Container c;
JButton btn;
JTextField tf;
public Test() //constructor
{

f=new JFrame("Swah!");
f.setBounds(50,50,300,300); //position and dimension of frame

c=f.getContentPane();// getting container of the frame
c.setLayout(new FlowLayout()); //if you do not use layout then only one 
//component will be visible to you.

btn=new JButton("OK");
tf=new JTextField(20);

c.add(btn);
c.add(tf);

f.setVisible(true);
f.setDefaultCloseOperation(f.EXIT_ON_CLOSE);
}

public static void main(String []val)
{
Test tobj=new Test();
}

}

you can use layouts according to you output, there are layouts like Flowlayout,GridLayout and GridBagLayout.

Hope this help you.