在 JFrame 或 JPanel java 上使用函数绘图

Question

I wanted to know if it is possible to use/make a function in another Class to draw an image/oval and then call it in the paint public void in our main Class.

If I have

public class Trydraw{
    
    public void drawrcircle(Graphics g){  

        g.setColor(Color.RED);      
        g.drawOval(0, 0, 20,20);  
        g.fillOval(0,0,20,20);    

    } 
    
}

And then call it here this way

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

public class Display extends JPanel{
   public static void main(String[]haha){
        
       JFrame frame = new JFrame();  
       frame.setSize(800, 500);  
       frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
       frame.setVisible(true);  

   }

   public void paint(Graphics g){

       super.paint(g); 
       Trydraw l = new Trydraw();
       l.drawrcircle(g);

   }
}

Thanks for your future help.

Answer 1

Yes you can, if I get your question correctly. Your sample code works for me if I add

frame.add(new Display());

to the end of your

public static void main(String[] haha)

method.

With your snippet the paint(g) method will never be called, because it will be executed with the initialization of the JPanel which will be initialized with the initialization the Display class (because of inheritance).

You probably want to create an instance of Display , which automatically initializes the JPanel with the overridden paint(g) method, thus the new Operator. As the constructor of a JPanel returns a JPanel , the constructor of Display returns a type of JPanel as well, which contains the red circle. This JPanel needs to be added with the add method to your original JFrame .