如何解决空错误才能成功检测冲突？

Question

我想实现一个像愤怒的小鸟使用swing的游戏，但是在一个简单的way.So中，每当用户点击射击按钮时，一个球就会被扔向三个方块。如果它们有交集，则应该打印出一条“冲突”消息。以下是我的类：

  import javax.swing.*;

public class ProjectileShooterTest {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
               ProjectileShooterPanel.createAndShowGUI();
            }
        });
    }
}

和：

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.Point2D;


class ProjectileShooterPanel extends JPanel {

    static Rectangle gerd;
    static Rectangle hadaf1;
    static Rectangle hadaf2;
    static Rectangle hadaf3;

    public static void createAndShowGUI() {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setSize(600, 600);
        final ProjectileShooter projectileShooter = new ProjectileShooter();
        ProjectileShooterPanel projectileShooterPanel = new ProjectileShooterPanel(
                projectileShooter);
        projectileShooter.setPaintingComponent(projectileShooterPanel);
        JPanel controlPanel = new JPanel(new GridLayout(1, 0));
        controlPanel.add(new JLabel("Angle"));
        final JSlider angleSlider = new JSlider(0, 90, 45);
        controlPanel.add(angleSlider);
        controlPanel.add(new JLabel("Power"));
        final JSlider powerSlider = new JSlider(0, 100, 50);
        controlPanel.add(powerSlider);
        JButton shootButton = new JButton("Shoot");
        shootButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                int angleDeg = angleSlider.getValue();
                int power = powerSlider.getValue();
                projectileShooter.setAngle(Math.toRadians(angleDeg));
                projectileShooter.setPower(power);
                projectileShooter.shoot(gerd,hadaf1,hadaf2,hadaf3);
            }
        });
        controlPanel.add(shootButton);
        f.getContentPane().setLayout(new BorderLayout());
        f.getContentPane().add(controlPanel, BorderLayout.NORTH);
        f.getContentPane().add(projectileShooterPanel, BorderLayout.CENTER);
        f.setVisible(true);
    }
private final ProjectileShooter projectileShooter;

public ProjectileShooterPanel(ProjectileShooter projectileShooter) {
        this.projectileShooter = projectileShooter;
}

@Override
protected void paintComponent(Graphics gr) {
        super.paintComponent(gr);
Graphics2D g = (Graphics2D) gr;
Projectile projectile = projectileShooter.getProjectile();
if (projectile != null) {
        g.setColor(Color.RED);
Point2D position = projectile.getPosition();
int x = (int) position.getX();
int y = getHeight() - (int) position.getY();
gerd = new Rectangle(x - 01, y - 10, 20, 20);
g.draw(gerd);
// g.fillOval(x-01, y-10, 20, 20);
}
        hadaf1 = new Rectangle(450, 450, 50, 50);
hadaf2 = new Rectangle(500, 450, 50, 50);
hadaf3 = new Rectangle(475, 400, 50, 50);
g.draw(hadaf1);
g.draw(hadaf2);
g.draw(hadaf3);


        }
        }

和：

import javax.swing.*;
import java.awt.*;
import java.awt.geom.AffineTransform;
import java.awt.geom.Point2D;

class ProjectileShooter {
    private double angleRad = Math.toRadians(45);
    private double power = 50;
    private Projectile projectile;
    private JComponent paintingComponent;

    void setPaintingComponent(JComponent paintingComponent) {
        this.paintingComponent = paintingComponent;
    }

    void setAngle(double angleRad) {
        this.angleRad = angleRad;
    }

    void setPower(double power) {
        this.power = power;
    }

    void shoot(Rectangle test, Rectangle test1, Rectangle test2, Rectangle test3) {

        Thread t = new Thread(new Runnable() {
            @Override
            public void run() {
                executeShot();
            }
        });
        t.setDaemon(true);
        t.start();
          if (test3.intersects(test))
          {System.out.println("collision");}

    }

    private void executeShot() {
        if (projectile != null) {
            return;
        }
        projectile = new Projectile();
        Point2D velocity = AffineTransform.getRotateInstance(angleRad).transform(
                new Point2D.Double(1, 0), null);
        velocity.setLocation(velocity.getX() * power * 0.5, velocity.getY() * power * 0.5);
        projectile.setVelocity(velocity);
        long prevTime = System.nanoTime();
        while (projectile.getPosition().getY() >= 0) {
            long currentTime = System.nanoTime();
            double dt = 3 * (currentTime - prevTime) / 1e8;
            projectile.performTimeStep(dt);
            prevTime = currentTime;
            paintingComponent.repaint();

            try {
                Thread.sleep(10);
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
                return;
            }
        }
        projectile = null;
        paintingComponent.repaint();


    }

    Projectile getProjectile() {
        return projectile;
    }
}

和：

import java.awt.geom.Point2D;

class Projectile {
    private final Point2D ACCELERATION = new Point2D.Double(0, -9.81 * 0.1);
    private final Point2D position = new Point2D.Double();
    private final Point2D velocity = new Point2D.Double();

    public Point2D getPosition() {
        return new Point2D.Double(position.getX(), position.getY());
    }

    public void setPosition(Point2D point) {
        position.setLocation(point);
    }

    public void setVelocity(Point2D point) {
        velocity.setLocation(point);
    }

    void performTimeStep(double dt) {
        scaleAddAssign(velocity, dt, ACCELERATION);
        scaleAddAssign(position, dt, velocity);
    }

    private static void scaleAddAssign(Point2D result, double factor, Point2D addend) {
        double x = result.getX() + factor * addend.getX();
        double y = result.getY() + factor * addend.getY();
        result.setLocation(x, y);
    }
}

但是当我执行它时，它没有声明冲突，并且我得到了这个错误：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at java.awt.Rectangle.intersects(Rectangle.java:786)
    at ProjectileShooter.shoot(ProjectileShooter.java:34)
    at ProjectileShooterPanel$1.actionPerformed(ProjectileShooterPanel.java:38)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
    at java.awt.Component.processMouseEvent(Component.java:6505)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
    at java.awt.Component.processEvent(Component.java:6270)
    at java.awt.Container.processEvent(Container.java:2229)
    at java.awt.Component.dispatchEventImpl(Component.java:4861)
    at java.awt.Container.dispatchEventImpl(Container.java:2287)
    at java.awt.Component.dispatchEvent(Component.java:4687)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
    at java.awt.Container.dispatchEventImpl(Container.java:2273)
    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)

我该怎么解决呢？请给我答案，我是爪哇新手。谢谢

Answer 1

在类ProjectileShooterPanel中，所有引用gerd、hadaf1、hadaf2、hadaf3均为空。

class ProjectileShooterPanel extends JPanel {
    static Rectangle gerd;
    static Rectangle hadaf1;
    static Rectangle hadaf2;
    static Rectangle hadaf3;

你应该在传递给shoot方法之前初始化它

projectileShooter.shoot(gerd,hadaf1,hadaf2,hadaf3);

Answer 2

在shootButton - ActionListener上执行actionPerformed的事件线程上执行交集检查。我猜你真正想要做的是重复执行这个检查，例如在你的移动循环的每一次迭代中，或者可能在每次重绘时。

我建议你将检查移动到一个你知道矩形是初始大小的地方-例如在你的paintComponent中。

你也应该认真研究一下同步和锁定。获得正确的Mutlithreading是编程中最好的工具之一，也是我们手中最强大的工具之一。