java - 在 Java 中创建我的第一个子类时遇到问题

Question

我正在尝试为我的 Java 课程制作一个 Breakout 游戏程序，其中包括一组彩色块（砖）。我已经成功完成了这项工作，但现在我的导师希望我们添加不同的 Bricks 子类。他想要的子类之一是 ColorBrick，它从 Brick 超类继承了它的所有行为，除了它有一个颜色数组，每 5 个滴答声就会改变一次。构造函数采用颜色数组而不是单一颜色。

这就是我的 Brick 超类：

package Breakout;

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

    public class Brick {

        public int x, y, i, j;
        public Color c;
        Brick[][] brick;

        public Brick() {
        }

        public Brick(Color c, Brick[][] brick, int i, int j) {
            this.c = c;
            this.brick = brick;
            this.x = i * 40;
            this.y = j * 10 + 50;
            this.i = i;
            this.j = j;



        }

        public void tick() {
        }

        public void paint(Graphics g) {
            g.setColor(c);
            g.fillRect(x, y, Breakout.brickWidth, Breakout.brickHeight);

        }

        public void hit(Ball b) {
            if (b.yThen > y + Breakout.brickHeight) {
                b.yv = -b.yv;
                b.yNow = 2 * (y + Breakout.brickHeight) - b.yNow;
            }
            if (b.yThen < y) {
                b.yv = -b.yv;
                b.yNow = 2 * (y) - b.yNow;
            }
            if (b.xThen > x + Breakout.brickWidth) {
                b.xv = -b.xv;
                b.xNow = 2 * (x + Breakout.brickWidth) - b.xNow;
            }
            if (b.xThen < x) {
                b.xv = -b.xv;
                b.xNow = 2 * (x) - b.xNow;
            }
            brick[i][j] = null;
        }
    }

这就是我到目前为止的 colorBrick 子类：

package Breakout;

import java.awt.Color;

    public class ColorBrick extends Brick {

        Color colors[] = {Color.red, Color.green, Color.blue, Color.yellow}; 

        public ColorBrick(Color[] colors, Brick[][] brick, int i, int j){
            this.colors = colors; 
            this.brick = brick; 
            this.i = i; 
            this.j = j; 
        }

        public void tick(){

        }

    }

在这一点上，我碰壁了，我不确定从这里该怎么做。我的导师说，由于某种原因，超类中的 tick 方法需要为空。如果它需要是空的，那么他为什么要我们把它放在那里？我也不确定我应该在子类 tick 方法中放什么。我的子类是否朝着正确的方向前进，或者到目前为止我所做的一切都是完全错误的？任何指导将不胜感激！

如果有用，这是我的主要突破代码：

package Breakout;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;
import javax.swing.JPanel;
import javax.swing.Timer;

    public class Breakout extends javax.swing.JFrame {

        public static final int fieldHeight = 600;
        public static final int fieldWidth = 400;
        public int diameter = 5;
        public int xNow = 200 - (diameter / 2);
        public int yNow = 300 - (diameter - 2);
        public int paddleWidth = 50;
        public int paddleHeight = 5;
        public int platform = 580;
        public static int mousex;
        public int mousey;
        public static int brickWidth = 40;
        public static int brickHeight = 10;
        public Random randoms = new Random();
        Brick[][] bricks = new Brick[arrayWide][arrayHigh];
        public static boolean startUp;
        public static int arrayWide = 10;
        public static int arrayHigh = 5;
        Ball ball = new Ball(200 - (diameter / 2), 20 /*300 - (diameter /2)*/, 0, 0, diameter, Color.white);
        Paddle myPaddle = new Paddle(platform, paddleWidth, paddleHeight);

        /**
         * Creates new form Breakout
         */
        public Breakout() {
            initComponents();
            clock.start();
        }

        public class MyPanel extends JPanel {

            @Override
            public void paint(Graphics g) {
                super.paint(g);
                if (startUp) {
                    ball.paint(g);
                }
                myPaddle.paint(g);

                for (int i = 0; i < arrayWide; i++) {
                    for (int j = 0; j < arrayHigh; j++) {
                        if (bricks[i][j] != null) {
                            bricks[i][j].paint(g);
                        }

                    }
                }
                // Insert code to paint the scene here.
                // Use methods in the Graphics class to do the painting
                // Remember coordinates use (0,0) at the top left

            }
        }
        public Timer clock = new Timer(50, new ActionListener() {  // 50ms delay between ticks
            public void actionPerformed(ActionEvent e) {
                tick();               // Write a method named tick to advance your game
                jPanel1.repaint();
            }
        });  // panel is the name of the JPanel that displays the game

        public void launchball() {
        }

        public void tick() {
            ball.move();
            Brick brick2 = brickAt(ball);
            if (brick2 != null) {
                brick2.hit(ball);
            }


            myPaddle.move(mousex);
            myPaddle.bounce(ball);
            System.out.println();


        }

        public Brick brickAt(Ball b) {
            int j = (int) (b.yNow - 50) / 10;
            int i = (int) (b.xNow / 40);
            if (i < arrayWide && i >= 0 && j < arrayHigh && j >= 0) {
                return (bricks[i][j]);



            }


            return null;
        }

        /**
         * This method is called from within the constructor to initialize the form.
         * WARNING: Do NOT modify this code. The content of this method is always
         * regenerated by the Form Editor.
         */
        @SuppressWarnings("unchecked")
        // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
        private void initComponents() {

            jPopupMenu1 = new javax.swing.JPopupMenu();
            jPanel2 = new javax.swing.JPanel();
            jPanel1 = new MyPanel();
            jLabel1 = new javax.swing.JLabel();
            start = new javax.swing.JButton();

            org.jdesktop.layout.GroupLayout jPanel2Layout = new org.jdesktop.layout.GroupLayout(jPanel2);
            jPanel2.setLayout(jPanel2Layout);
            jPanel2Layout.setHorizontalGroup(
                jPanel2Layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
                .add(0, 100, Short.MAX_VALUE)
            );
            jPanel2Layout.setVerticalGroup(
                jPanel2Layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
                .add(0, 100, Short.MAX_VALUE)
            );

            setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

            jPanel1.setBackground(new java.awt.Color(0, 0, 0));
            jPanel1.addMouseMotionListener(new java.awt.event.MouseMotionAdapter() {
                public void mouseMoved(java.awt.event.MouseEvent evt) {
                    mouseMove(evt);
                }
            });

            org.jdesktop.layout.GroupLayout jPanel1Layout = new org.jdesktop.layout.GroupLayout(jPanel1);
            jPanel1.setLayout(jPanel1Layout);
            jPanel1Layout.setHorizontalGroup(
                jPanel1Layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
                .add(0, 400, Short.MAX_VALUE)
            );
            jPanel1Layout.setVerticalGroup(
                jPanel1Layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
                .add(0, 600, Short.MAX_VALUE)
            );

            jLabel1.setFont(new java.awt.Font("Hobo Std", 1, 24)); // NOI18N
            jLabel1.setForeground(new java.awt.Color(153, 51, 255));
            jLabel1.setText("Breakout");

            start.setFont(new java.awt.Font("Hobo Std", 0, 13)); // NOI18N
            start.setForeground(new java.awt.Color(255, 51, 0));
            start.setText("Start");
            start.addActionListener(new java.awt.event.ActionListener() {
                public void actionPerformed(java.awt.event.ActionEvent evt) {
                    startActionPerformed(evt);
                }
            });

            org.jdesktop.layout.GroupLayout layout = new org.jdesktop.layout.GroupLayout(getContentPane());
            getContentPane().setLayout(layout);
            layout.setHorizontalGroup(
                layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
                .add(layout.createSequentialGroup()
                    .add(layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
                        .add(layout.createSequentialGroup()
                            .add(164, 164, 164)
                            .add(jLabel1))
                        .add(layout.createSequentialGroup()
                            .add(15, 15, 15)
                            .add(jPanel1, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE))
                        .add(layout.createSequentialGroup()
                            .add(175, 175, 175)
                            .add(start)))
                    .addContainerGap(17, Short.MAX_VALUE))
            );
            layout.setVerticalGroup(
                layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
                .add(layout.createSequentialGroup()
                    .add(16, 16, 16)
                    .add(jLabel1)
                    .addPreferredGap(org.jdesktop.layout.LayoutStyle.UNRELATED)
                    .add(jPanel1, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE)
                    .addPreferredGap(org.jdesktop.layout.LayoutStyle.UNRELATED)
                    .add(start)
                    .addContainerGap(10, Short.MAX_VALUE))
            );

            pack();
        }// </editor-fold>                        

        private void mouseMove(java.awt.event.MouseEvent evt) {                           
            mousex = evt.getX();
            mousey = evt.getY();
        }                          

        private void startActionPerformed(java.awt.event.ActionEvent evt) {                                      

            startUp = true;
            ball.xNow = 200 - (diameter / 2);
            ball.yNow = 300 - (diameter - 2);
            ball.xv = 0;
            ball.yv = 8;
            for (int i = 0; i < arrayWide; i++) {
                for (int j = 0; j < arrayHigh; j++) {
                    if ((j % 2 == 0 && i % 2 == 0) || (j % 2 == 1 && i % 2 == 1)) {
                        bricks[i][j] = new Brick(Color.magenta, bricks, i, j);
                    } else {
                        bricks[i][j] = new Brick(Color.gray, bricks, i, j);
                    }

                }
            }
        }                                     

        /**
         * @param args the command line arguments
         */
        public static void main(String args[]) {
            /* Set the Nimbus look and feel */
            //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
            /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
             * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
             */
            try {
                for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                    if ("Nimbus".equals(info.getName())) {
                        javax.swing.UIManager.setLookAndFeel(info.getClassName());
                        break;
                    }
                }
            } catch (ClassNotFoundException ex) {
                java.util.logging.Logger.getLogger(Breakout.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
            } catch (InstantiationException ex) {
                java.util.logging.Logger.getLogger(Breakout.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
            } catch (IllegalAccessException ex) {
                java.util.logging.Logger.getLogger(Breakout.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
            } catch (javax.swing.UnsupportedLookAndFeelException ex) {
                java.util.logging.Logger.getLogger(Breakout.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
            }
            //</editor-fold>

            /* Create and display the form */
            java.awt.EventQueue.invokeLater(new Runnable() {
                public void run() {
                    new Breakout().setVisible(true);
                }
            });
        }

Answer 1

由于这听起来像 homework.classwork，我不打算详细介绍。

据推测，某些东西（待定）将每 5 秒（或定期）调用一次 tick()。正常人Brick什么都不做。您ColorBrick应该每 5 秒更改一次颜色。不知何故，它需要知道它的当前颜色并更改为下一个颜色。

Answer 2

需要有一个空tick方法，Brick以便另一个类只需要处理Bricks；调用的类tick不需要知道它是 aBrick还是 a ColorBrick。的行为tick由运行时类指定；这就是多态性——相关类对同一方法调用做出不同反应的能力。

子类tick方法需要跟踪已生成的刻度数。需要时，它会更改 Color 变量c。

我可能会在您的ColorBrick构造函数中进行另一项更改：利用super调用超类构造函数，以免重复您的代码。

此外，声明您的实例变量（c、x、y等）protected，以便只有类本身和子类可以直接访问它们。

Answer 3

tick 方法需要存在于超类中，因为我猜测其意图是对于存在的每个 Brick，都会调用 tick() （可能在主 Breakout 类中，可能在循环中）。超类中的 tick() 方法指定了“默认”行为，即什么也不做。对于您的 ColorBrick 类，当调用 tick 时，颜色需要每五个 tick 改变一次，因此您需要在子类 (ColorBrick) 中指定这种特殊的行为情况。

为此，ColorBrick 需要一种方法来记录调用 tick() 的次数。一旦添加了一些可以执行此操作的代码，您就可以考虑在某些刻度上更改 ColorBrick 的颜色：您的 ColorBrick 已经“知道”其当前颜色，因为它从具有 Color 属性的 Brick 扩展而来（ c)，因此这是在某些刻度上更改该值的情况。

我故意含糊其辞，因为我不想为你完成你的任务，但请随时提出任何问题。

Answer 4

您需要以如下方式实现您的tick方法ColorBrick：

private int i = 0;
public void tick(){
    c = colors[i++ % colors.length];
}

现在，在制作图形应用程序时，您也可以简单地使用Brick该类来创建ColorBricks。例如，添加多个砖块来制作墙壁：

Brick[][] wall = new Brick[5][5];

上面数组中的一些Brick可能是ColorBrick. 这允许有一个通用接口，即tick()每个Brick对象的方法。但是对于ColorBrick这种方法实际上改变了Brickwhere-as in other的颜色，Brick它什么也不做！

你可以做更多的事情，比如DancingBrick在每个tick. 您的图形实现不需要为了添加不同类型而进行大幅更改，Brick因为它使用基本类型 as Brick。