Java Paintcomponent未调用

Question

public class AnaMetod {

    public static void main(String[] args) {
        Grafik2D g2 = new Grafik2D(10, 50,  "StackOverFlow");
    }
}


package kibAr2D;

import java.awt.Graphics;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class Grafik2D extends JPanel {
    public static int a, b = 0;
    public static String c = "";

    public Grafik2D(int a, int b, String c) {
        this.a = a;
        this.b = b;
        this.c = c;
        JFrame j = new JFrame();
        j.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        j.setTitle("kibAr");
        j.setBounds(150, 200, 613, 253);
        j.setVisible(true);
    }

    public void paintComponent(Graphics g){
        super.paintComponents(g);
        g.drawString(c, a, b);

    }
}

I cant understand why the paint method dont invoke? Maybe when JFrame create then automaticaly paintComponent and paint method invoke.. So how i can replace this problem?

Sory for my bad english..

Answer 1

The problem is that you have created an empty JFrame , but you have not added any components to it. Since your Grafik2D class is a JPanel , you need to add it to the frame with the line:

j.add(this);

in the constructor.

Answer 2

There are two problems with your code:

1.) An instance of your Grafik2D class needs to be in the visual tree. You should add it like this:

public Grafik2D(int a, int b, String c) {
     // ...
     JFrame j = new JFrame();
     // ...
     j.add(this);
}

2.) You should either delete the call to paintComponents or correct the spelling:

super.paintComponent(g);