Question

我正在创造一个巨魔＆＃39;就像在YouTube视频中使用的应用程序一样，我希望JFrame每1/2秒在屏幕上跳转一次。

继承我的代码：

package troll1;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;

import javax.swing.JFrame;
import javax.swing.Timer;

public class troll extends JFrame implements ActionListener{
    private static final long serialVersionUID = 1L;

    public static void main(String args[]) {
        troll w1 = new troll();
        w1.setVisible(true);
        w1.setSize(500,500);
    }

    public Random ran;
    public int random;
    public troll w1;
    public Timer t;

    public troll() {
        Timer t = new Timer(500, this);
        t.start();

    }

    @Override
    public void actionPerformed(ActionEvent arg0) {
        Random ran = new Random();

        for(int counter=1; counter<=1;counter++) {
            int random = 1+ran.nextInt(500);
            w1.setLocation(random, random);
        }

    }

}

问题是，当我运行此代码时，我收到错误消息

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at troll1.troll.actionPerformed(troll.java:37)
    at javax.swing.Timer.fireActionPerformed(Unknown Source)
    at javax.swing.Timer$DoPostEvent.run(Unknown Source)
    at java.awt.event.InvocationEvent.dispatch(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$500(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)

此外，一旦我的错误消失了，我就会这样做，以便JFrame在整个屏幕上跳跃，而不仅仅是500,500及以下。

Answer 1

w1变量始终为null永远不会被赋值。你可以在actionPerformed中使用它来使它以这种方式工作

 @Override
public void actionPerformed(ActionEvent arg0) {
    Random ran = new Random();

    for(int counter=1; counter<=1;counter++) {
        int random = 1+ran.nextInt(500);
        this.setLocation(random, random);
    }

}

.setLocation不使用计时器

1 个答案: