Question

线程中的异常＆＃34; AWT-EventQueue-0＆＃34;显示java.lang.NullPointerException 在Snooker.paint（Snooker.java:34）

这是我所得到的错误。

以下是代码：

主类：

import java.awt.BorderLayout;    
import java.awt.Color;    
import java.awt.Graphics;    
import javax.swing.JFrame;    
import javax.swing.JPanel;

public class Snooker extends JPanel {

    public static final int WIDTH = 900;
    public static final int HEIGHT = 450;
    public static final Color c = Color.black;
    public static final int SIZE_ball = 10;

    private Table table;
    private Ball ball;
    private Cue cue;
    public Snooker() {
        table = new Table(0,0,c,WIDTH,HEIGHT);
        ball = new Ball(150,150,Color.RED,SIZE_ball);
    }

    public void paint(Graphics g) {
        super.paint(g);      
        table.drawTableOn(g);             
        ball.drawBallOn(g);            
        cue.drawCueOn(g);
    }
    public static void main(String[] args) throws InterruptedException {
        JFrame frame = new JFrame("Snooker");
        frame.setLayout(new BorderLayout());
        frame.setSize(WIDTH, HEIGHT);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);     
        Snooker game = new Snooker();     
        frame.add(game);
        frame.setVisible(true);
        game.requestFocusInWindow();
    }
}

图形类：

import java.awt.Color;    
import java.awt.Graphics;

public class GraphicsItem {

    protected int x,y;
    protected Color color;
    private static final int SIZE_tableX = 900;
    private static final int SIZE_Cue = 30;
    public static final int R_ball = 5;
    public static int CoorY = 150;
    public static int CoorX = 150;


    public GraphicsItem(int x, int y, Color color) {
        this.x = x;
        this.y = y;
        this.color = color;
    }
    public int getX() {
        return x;
    }
    public int getY() {
        return y;
    }
    public void setX(int x) {
        this.x = x;
    }
    public void setY(int y) {
        this.y = y;
    }

    public void moveBallBy(int dx, int dy) {
        x += dx;
        y += dy;
    }

    public void drawTableOn(Graphics g) {
        g.setColor(color.BLACK);
        g.fillRect(x, y, SIZE_tableX, SIZE_tableX/2);
    }

    public void drawBallOn(Graphics g) {
        g.setColor(color.BLACK);
        g.fillOval(x,y,R_ball,R_ball);
    }

    public void drawCueOn(Graphics g) {
        g.setColor(color.BLACK);
        g.drawLine(x,y,SIZE_Cue,SIZE_Cue);          
    }
}

还有5个班级。 Cue，Ball，Table和CueBall（extends Ball），BroadCloth（扩展表）。他们的对象只有态度。

建议解决？

Answer 1

你必须在类Snooker的构造函数中初始化cue。

你的构造函数应该是：

public Snooker() {
    table = new Table(0,0,c,WIDTH,HEIGHT);
    ball = new Ball(150,150,Color.RED,SIZE_ball);
    cue = new Cue( ... );
}

就目前而言，cue尚未实例化，并在您尝试访问其方法时抛出NullPointerException。

＆＃34; AWT-EventQueue的-0＆＃34;游戏试用代码出错

1 个答案: