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通過鼠標單擊繪制圓畫問題

[英]Circle draw by mouse click issue

 原文  2013-11-04 21:58:53  0   1    java/ swing/ jframe/ mouseevent

問題描述

我正在學習Java幾周了，但是“項目”有問題。

我正在嘗試編寫一個簡單的（顯然不適合我）程序，該程序通過鼠標單擊在單擊鼠標的坐標上在畫布上繪制一個圓！

這是我的代碼：

MyGame3.java包mygame3; 

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import javax.swing.JFrame;

public class MyGame3 extends JFrame{
    int WIDTH, HEIGHT;

    Image dbImage;
    Graphics dbg;

    static ArrayList<Circle> circles;

    public MyGame3(){
        WIDTH = 600;
        HEIGHT = 600;

        setSize(WIDTH, HEIGHT);
        setTitle("My Game 3");
        setBackground(Color.white);
        setResizable(false);
        setVisible(true);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        addMouseListener(new MouseAdapter() {
            public void mousePressed(MouseEvent e){
                System.out.println(e.getX() + " " + e.getY());
                circles.add(new Circle(e.getX(), e.getY()));
            }
        });
    }

    @Override
    public void paint(Graphics g){
        dbImage = createImage(getWidth(), getHeight());
        dbg = dbImage.getGraphics();
        draw(dbg);
        g.drawImage(dbImage, 0, 0, this);
    }

    public void draw(Graphics g){
        if (circles.size() > 0){
            for (Circle c: circles){
                c.draw(g);
            }
            repaint();
        }

    }

    public static void main (String[] args){
        MyGame3 main = new MyGame3();

        if (circles.size() > 0){
            for (Circle c: circles){
                Thread circle = new Thread(c);
                circle.start();
            }
        }
    }
}

Circle.java： 

package mygame3;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.geom.Ellipse2D;

public class Circle implements Runnable{    

    Ellipse2D circle;

    public Circle(int x, int y){

        circle = new Ellipse2D.Double(x, y, 30, 30);
    }

    public void draw (Graphics g){
        g.setColor(Color.blue);
        g.drawOval((int)circle.getX(),
                   (int)circle.getY(),
                   (int)circle.getWidth(),
                   (int)circle.getHeight());
    }

    @Override
    public void run() {
        try{
            while(true){
                Thread.sleep(2);
            }
        }
        catch(Exception e){
            System.err.println(e.getMessage());
        }
    }
}

這是我在屏幕上單擊兩次時遇到的錯誤： 

run:
Exception in thread "main" java.lang.NullPointerException
    at mygame3.MyGame3.main(MyGame3.java:59)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at mygame3.MyGame3.draw(MyGame3.java:47)
    at mygame3.MyGame3.paint(MyGame3.java:42)
    at javax.swing.RepaintManager$3.run(RepaintManager.java:819)
    at javax.swing.RepaintManager$3.run(RepaintManager.java:796)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:796)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:769)
    at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:718)
    at javax.swing.RepaintManager.access$1100(RepaintManager.java:62)
    at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1677)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:733)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:694)
    at java.awt.EventQueue$3.run(EventQueue.java:692)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:703)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at mygame3.MyGame3.draw(MyGame3.java:47)
    at mygame3.MyGame3.paint(MyGame3.java:42)
    at javax.swing.RepaintManager$3.run(RepaintManager.java:819)
    at javax.swing.RepaintManager$3.run(RepaintManager.java:796)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:796)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:769)
    at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:718)
    at javax.swing.RepaintManager.access$1100(RepaintManager.java:62)
    at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1677)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:733)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:694)
    at java.awt.EventQueue$3.run(EventQueue.java:692)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:703)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
245 386
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at mygame3.MyGame3$1.mousePressed(MyGame3.java:33)
    at java.awt.Component.processMouseEvent(Component.java:6502)
    at java.awt.Component.processEvent(Component.java:6270)
    at java.awt.Container.processEvent(Container.java:2229)
    at java.awt.Window.processEvent(Window.java:2022)
    at java.awt.Component.dispatchEventImpl(Component.java:4861)
    at java.awt.Container.dispatchEventImpl(Container.java:2287)
    at java.awt.Window.dispatchEventImpl(Window.java:2719)
    at java.awt.Component.dispatchEvent(Component.java:4687)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:735)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:694)
    at java.awt.EventQueue$3.run(EventQueue.java:692)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
    at java.awt.EventQueue$4.run(EventQueue.java:708)
    at java.awt.EventQueue$4.run(EventQueue.java:706)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:705)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
245 386
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at mygame3.MyGame3$1.mousePressed(MyGame3.java:33)
    at java.awt.Component.processMouseEvent(Component.java:6502)
    at java.awt.Component.processEvent(Component.java:6270)
    at java.awt.Container.processEvent(Container.java:2229)
    at java.awt.Window.processEvent(Window.java:2022)
    at java.awt.Component.dispatchEventImpl(Component.java:4861)
    at java.awt.Container.dispatchEventImpl(Container.java:2287)
    at java.awt.Window.dispatchEventImpl(Window.java:2719)
    at java.awt.Component.dispatchEvent(Component.java:4687)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:735)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:694)
    at java.awt.EventQueue$3.run(EventQueue.java:692)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
    at java.awt.EventQueue$4.run(EventQueue.java:708)
    at java.awt.EventQueue$4.run(EventQueue.java:706)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:705)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
BUILD SUCCESSFUL (total time: 3 seconds)

感謝您的任何答復！

1 個解決方案

解決方案1
 1  2013-11-04 22:10:35

讓我們從...開始

我看不到任何初始化circles ArrayList ...

然后繼續...

您應該避免覆蓋頂層容器的paint ，除了它們不是雙重緩沖的事實之外，它們通常還涉及構成頂層容器的一系列其他組件。

相反，您應該創建一個自定義組件，例如從JPanel擴展，並覆蓋它的paintComponent方法。 Swing組件是雙緩沖的，因此您不需要為此做任何特殊的事情。

我也看不出為什么Circle應該需要實現Runnable 。

如果要執行某種動畫，則應使用單個線程來修改整個狀態，然后將其渲染為單個步驟。 這樣可以使事物保持同步，並避免使系統餓死。

您還應該避免從任何paintXxx方法中修改或更新UI的狀態。 例如，不要在繪制方法中調用repaint ...

請看表演自定義繪畫以了解更多詳細信息

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