如何在此程序中更改 JFrame 的背景颜色？

Question

I use the setBackground() method in the Driver Class to change the background color but it does not work.

package paint1;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.util.ArrayList;
import javax.swing.JButton;
import javax.swing.JPanel;

/**
 *
 * @author Rehan Shakir
 */
public class PaintPanel extends JPanel {

    private final ArrayList<Point> point = new ArrayList<>();
    private Color color;
    private final JButton red,blue,yellow,green,gray;
    private int x = 0;
    private int y = 0;




    public PaintPanel()
    {

         setLayout(null);



         red = new JButton("   Red  ");
        red.setBounds(0, 0, 80, 50);
        red.setBackground(Color.red);
        add(red);

        blue = new JButton("  Blue  ");
        blue.setBounds(82,0 , 80, 50);
        blue.setBackground(Color.BLUE);
        add(blue);

         yellow = new JButton("Yellow");
         yellow.setBounds(163,0 , 80, 50);
        yellow.setBackground(Color.yellow);
        add(yellow);

         green = new JButton(" Green");
         green.setBounds(242,0 , 80, 50);
        green.setBackground(Color.green);
        add(green);

         gray = new JButton("  Gray ");
         gray.setBounds(322,0 , 80, 50);
        gray.setBackground(Color.gray);
        add(gray);


        handler h = new handler();
        red.addActionListener(h);
        blue.addActionListener(h);
        yellow.addActionListener(h);
        green.addActionListener(h);
        gray.addActionListener(h);

        setBackground(Color.RED);



        addMouseMotionListener(
        new MouseMotionAdapter()
        {

            @Override
            public void mouseDragged(MouseEvent e)
                {
                   x = e.getX();
                   y = e.getY();
                   repaint();

                }


        }
               );

    }
    private class handler implements ActionListener
    {


                  @Override
                  public void actionPerformed(ActionEvent e)
                {

                  String s = e.getActionCommand();
                  if(s.equals("   Red  "))
                      color = Color.RED;
                  else if(s.equals("  Blue  "))
                      color = Color.blue;
                  else if(s.equals("Yellow"))
                      color = Color.yellow;
                  else if(s.equals(" Green"))
                      color = Color.green;
                  else if(s.equals("  Gray "))
                      color = Color.gray;


                }


    }
    @Override
        public void paintComponent(Graphics g)
        {

          g.setColor(color);
          g.fillOval(x, y, 20, 5);

        }

    }

<<>> Here, I use the setBackground() method to change the color but it does not work.

package paint1;

import java.awt.BorderLayout;
import java.awt.Color;
import javax.swing.JFrame;
import javax.swing.JLabel;

/**
 *
 * @author Rehan Shakir
 */
public class Paint1 {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here

        JFrame Jf = new JFrame("A Simple Paint Program");

        PaintPanel f = new PaintPanel();
        f.setBackground(Color.red);  //To Change BACKGROUND COLOR


        Jf.add(f,BorderLayout.CENTER);

        Jf.add(new JLabel("Drag The Mouse to Draw"),BorderLayout.SOUTH);

        Jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Jf.setBackground(Color.black);
        Jf.setVisible(true);
        Jf.setSize(800,600);


    }

}

Please provide me the solution, how can I change the background color of my JFrame? I just want to make the background color of JFrame from the default color to White color.

Answer 1

You've forget to call the parent method in paintComponent .

    @Override
    public void paintComponent(Graphics g)
    {
      super.paintComponent(g); // add this line to consider background!!!
      g.setColor(color);
      g.fillOval(x, y, 20, 5);

    }

Important : Don't use setBounds() but rather learn the LayoutManager concept . This will help you to make your UI independed to OS, display resolution and window resizing.