使用paint（g）和run（）绘制点

Question

What I want to do is once I pressed the button "GO", it will paint/draw 3 ovals with different coordinates. I've tried repainting but seems it doesn't work. It only shows one oval which is the last oval. I want it to stack up and append the ovals.

Here's my code:

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

public class Test extends JFrame implements ActionListener{
JButton button;
int[] itoken;
int x,y;

public Test() {
super("Test");
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setSize(600,500);
this.setVisible(true);
this.setResizable(true);
this.setLayout(null);

button= new JButton("GO");
button.setBounds(500, 100, 50,50);

this.add(button);
button.addActionListener(this);
}

public void actionPerformed(ActionEvent e){ 
    if(e.getSource()==button){
        String text= "200 300 250 150 400 100";
        String[] token= text.split("\\W");
        itoken= new int[token.length];
        int i=0;
        for (String str : token){
            itoken[i++] = Integer.parseInt(str);
        }
        for(i=0; i<itoken.length; i++)
        System.out.println(itoken[i]);
    run();
    }
}

public void paint(Graphics g) {
    super.paint(g);
        g.drawOval(x - 5, y - 5, 10, 10);
}   

public void run(){
    int i=0;        
    while(i<itoken.length-1){
        repaint();
        x=itoken[i];
        y=itoken[i+1];
        i++;
    }
}

public static void main(String[] args) {
    Test test = new Test(); 
}
}

Answer 1

Note - I was working on this answer right before you deleted your previous question, so the answer may see a little off in terms of the new code you posted in this question, but it gets you towards the same goal.

1. Don't initialize everthing in the actionPerformed . You're getting a NullPointerException because paint is called by the frame implicitly before the array is initialized. What I did was create a method to initialize it

    int[] iToken = initArray(); ... private int[] initArray() { String text = "200 300 250 150 400 100"; String[] token = text.split("\\\\W"); int[] itoken = new int[token.length]; int i = 0; for (String str : token) { itoken[i++] = Integer.parseInt(str); } return itoken; } 

2. Don't paint on top level containers like JFrame . Instead us a JPanel or JCompoent and override paintComponent , and override getPreferredSize() in your JPanel so you won't have to set the size of your JFrame . Just pack() it.

3. Run Swing apps from the Event Dispatch Thread like this

    public static void main(String[] args) { SwingUtilitiies.invokeLater(new Runnable(){ public void run(){ new Test(); } }); } 

4. You never add your button to the frame.

5. Don't use a null layout. Use Layout Managers .

6. Add you components, then call setVisible

---

Here's the running refactored code

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

public class Test extends JFrame implements ActionListener {

    JButton button;
    boolean paint = false;
    int x, y;
    int[] iToken = initArray();

    public Test() {

        super("Test");

        button = new JButton("GO");
        button.setBounds(500, 100, 50, 50);
        button.addActionListener(this);
        add(button, BorderLayout.SOUTH);
        add(new DrawPanel());

        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.pack();
        this.setVisible(true);
        this.setResizable(true);

    }

    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == button) {
            paint = true;
            repaint();
        }
    }

    private int[] initArray() {
        String text = "200 300 250 150 400 100";
        String[] token = text.split("\\W");
        int[] itoken = new int[token.length];
        int i = 0;
        for (String str : token) {
            itoken[i++] = Integer.parseInt(str);
        }
        return itoken;
    }

    public class DrawPanel extends JPanel {

        public void paintComponent(Graphics g) {
            super.paintComponent(g);

            if (paint) {
                for (int i = 0; i < iToken.length; i += 2) {
                    x = iToken[i];
                    y = iToken[i + 1];
                    g.drawOval(x - 5, y - 5, 10, 10);
                }
            }
        }

        public Dimension getPreferredSize() {
            return new Dimension(500, 500);
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new Test();
            }
        });
    }
}