添加面板和框架后，paint() 不起作用

Question

I am making kind of my paint that creates shapes, it worked fine until I added layers(panel and frame), now the shapes aren't visible on button press I assume it is under the layers?i tried using paintComponent and revalidate etc and still couldn't get it to appear

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class Main2 extends JPanel implements ActionListener {

    private static Square mySquare;
    private static Circle myCircle;
    private static Color myColor;
    public boolean SquareCheck;
    public boolean CircleCheck;
    JButton buttonSquare;
    JButton buttonCircle;
    JFrame frame;
    JPanel panel;

    public void paint(Graphics g) {
        if (SquareCheck) {
            g.setColor(myColor);
            g.fillRect(mySquare.x, mySquare.y, mySquare.width, mySquare.length);
        } else if (CircleCheck) {
            g.setColor(myColor);
            g.fillOval(myCircle.x, myCircle.y, myCircle.width, myCircle.length);
        }
    }

    public void start() {
        frame = new JFrame();
        panel = new JPanel();

        //setLayout(new BorderLayout());

        buttonSquare = new JButton("■");
        buttonCircle = new JButton("●");

        buttonSquare.setPreferredSize(new Dimension(200, 20));
        buttonCircle.setPreferredSize(new Dimension(200, 20));

        buttonCircle.addActionListener(this);
        buttonSquare.addActionListener(this);
        //add(buttonCircle, BorderLayout.NORTH);
        //add(buttonSquare, BorderLayout.SOUTH);
        JToggleButton red = new JToggleButton();
        panel.add(buttonCircle);
        panel.add(buttonSquare);
        frame.add(panel);
        frame.setSize(500, 500);
        frame.setVisible(true);

    }

    public void actionPerformed(ActionEvent e) {

        if (e.getSource() == buttonSquare) {
            SquareCheck = true;
        } else if (e.getSource() == buttonCircle) {
            CircleCheck = true;
        }
        repaint();

    }
    public static void main(String[] args) {
        mySquare = new Square(30, 50, 50, 50);
        myCircle = new Circle(60, 100, 50, 50);
        myColor = Color.red;
        Main2 x = new Main2();
        x.start();

    }
}

Basiclly the buttons changes the boolean then the repaint is called and based on the boolean it draws either a cirlce or a square,the code worked before adding frame and panel

Answer 1

Your paint method is a method of the Main2 class, but you never add a Main2 instance to the JFrame or to any component that goes into the JFrame, and so the Main2 instance will never be displayed, and the Swing painting manager will never call its paint method.

For starters, get rid of this variable, panel = new JPanel(); and every place you use panel , substitute this . This way you'll be working with a correct Main2 instance and adding it to the GUI.

Other issues:

• You need to call the super's equivalent painting method in your override on its first line
• Override paintComponent, not paint, and yes call super.paintComponenet(g); in this override
• You will want to learn and use Java naming conventions . Variable names should all begin with a lower letter while class names with an upper case letter. Learning this and following this will allow us to better understand your code, and would allow you to better understand the code of others.
• For safety's sake, add the @Override annotation above any method that you think may be overriding a parent method (such as paint), to make sure that you are doing it correctly.

For example:

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

@SuppressWarnings("serial")
public class Main2 extends JPanel implements ActionListener {

    private static Square mySquare;
    private static Circle myCircle;
    private static Color myColor;
    private JToggleButton buttonSquare;
    private JToggleButton buttonCircle;
    JFrame frame;

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        if (buttonSquare.isSelected()) {
            g.setColor(myColor);
            g.fillRect(mySquare.x, mySquare.y, mySquare.width, mySquare.length);
        } 
        if (buttonCircle.isSelected()) {
            g.setColor(myColor);
            g.fillOval(myCircle.x, myCircle.y, myCircle.width, myCircle.length);
        }
    }

    public Main2() {
        frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        buttonSquare = new JToggleButton("■");
        buttonCircle = new JToggleButton("●");

        buttonCircle.addActionListener(this);
        buttonSquare.addActionListener(this);

        this.add(buttonCircle);
        this.add(buttonSquare);
        frame.add(this);
        frame.setSize(500, 500);
        frame.setVisible(true);
    }

    public void actionPerformed(ActionEvent e) {
        repaint();
    }

    public static void main(String[] args) {
        mySquare = new Square(30, 50, 50, 50);
        myCircle = new Circle(60, 100, 50, 50);
        myColor = Color.red;
        new Main2();
    }
}

class MyShape {
    public int x, y, width, length;

    public MyShape(int x, int y, int width, int length) {
        this.x = x;
        this.y = y;
        this.width = width;
        this.length = length;
    }

}