向Java小程序添加按钮

使用这段代码，我想在页面上添加一个按钮，当游戏状态为死亡或胜利时显示。此按钮将允许用户重新开始或进入下一个级别。我的动作监听器尚未完全编码，因为我甚至无法让按钮在页面上可见。我曾尝试使用

setLayout(new FlowLayout());
this.add(sOver);
sOver = new Button("Start Over");
sOver.addActionListener(this);

但是当游戏改变状态时，这会导致一个错误

 package androidGame;

import java.applet.Applet;
import java.awt.event.*;
import java.applet.AudioClip;
import java.awt.Button;
import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.Font;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.ArrayList;
import java.util.Random;
import java.net.*;

import javax.sound.sampled.AudioInputStream;
import javax.sound.sampled.AudioSystem;
import javax.sound.sampled.Clip;




import androidGame.framework.Animation;

import java.applet.Applet;
import java.applet.AudioClip;
import java.net.URL;

public class StartingClass extends Applet implements Runnable, KeyListener, ActionListener {

    enum GameState {
        Running, Dead, Win
    }

    GameState state = GameState.Running;

    private static Robot robot;
    public static Heliboy hb, hb2, hb3, hb4, hb5, hb6, hb7, hb8, hb9, hb10, hb11, hb12, hb13, hb14, hb15, hb16;
    public static int score = 0;
    public static int rHealth = 120;
    private Font font = new Font(null, Font.BOLD, 30);

    private Image image, currentSprite, character, character2, character3,
            characterDown, characterJumped, background, heliboy, heliboy2,
            heliboy3, heliboy4, heliboy5;

    public static Image tilegrassTop, tilegrassBot, tilegrassLeft,
            tilegrassRight, tiledirt, tilefire, tiledoor;

    private Graphics second;
    private URL base;
    private static Background bg1, bg2;
    private Animation anim, hanim;
    int level = 1;
    AudioClip clip;
    Button next, sOver;

    private ArrayList<Tile> tilearray = new ArrayList<Tile>();

    @Override

    public void init() {

        setSize(800, 480);
        setBackground(Color.BLACK);
        setFocusable(true);
        addKeyListener(this);
        Frame frame = (Frame) this.getParent().getParent();
        frame.setTitle("Robot Mania");
        try {
            base = getDocumentBase();
        } catch (Exception e) {
            // TODO: handle exception
        }

        // Image Setups
        character = getImage(base, "data/character.png");
        character2 = getImage(base, "data/character2.png");
        character3 = getImage(base, "data/character3.png");

        characterDown = getImage(base, "data/down.png");
        characterJumped = getImage(base, "data/jumped.png");

        heliboy = getImage(base, "data/heliboy.png");
        heliboy2 = getImage(base, "data/heliboy2.png");
        heliboy3 = getImage(base, "data/heliboy3.png");
        heliboy4 = getImage(base, "data/heliboy4.png");
        heliboy5 = getImage(base, "data/heliboy5.png");

        background = getImage(base, "data/spacebackground.png");

        tiledirt = getImage(base, "data/tiledirt.png");
        tilegrassTop = getImage(base, "data/tilegrasstop.png");
        tilegrassBot = getImage(base, "data/tilegrassbot.png");
        tilegrassLeft = getImage(base, "data/tilegrassleft.png");
        tilegrassRight = getImage(base, "data/tilegrassright.png");
        tilefire = getImage(base, "data/tilefire.png");
        tiledoor = getImage(base, "data/tiledoor.png");

        anim = new Animation();
        anim.addFrame(character, 1250);
        anim.addFrame(character2, 50);
        anim.addFrame(character3, 50);
        anim.addFrame(character2, 50);

        hanim = new Animation();
        hanim.addFrame(heliboy, 100);
        hanim.addFrame(heliboy2, 100);
        hanim.addFrame(heliboy3, 100);
        hanim.addFrame(heliboy4, 100);
        hanim.addFrame(heliboy5, 100);
        hanim.addFrame(heliboy4, 100);
        hanim.addFrame(heliboy3, 100);
        hanim.addFrame(heliboy2, 100);




        currentSprite = anim.getImage();
    }

    @Override
    public void start() {
        //Sound.MAIN.loop();
        bg1 = new Background(0, 0);
        bg2 = new Background(2160, 0);
        robot = new Robot();
        // Initialize Tiles
        try {
            loadMap("data/map"+ level +".txt");
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        Random random = new Random();
        int randomInt = random.nextInt(500);

        hb = new Heliboy(700, 360);
        hb2 = new Heliboy(900 + randomInt, 360);
        hb3 = new Heliboy(2300 + randomInt, 360);
        hb4 = new Heliboy(2900 + randomInt, 360);
        hb5 = new Heliboy(3400 + randomInt, 360);
        hb6 = new Heliboy(3900 + randomInt, 360);
        hb7 = new Heliboy(4300 + randomInt, 360);
        hb8 = new Heliboy(4700 + randomInt, 360);
        hb9 = new Heliboy(5000 + randomInt, 360);
        hb10 = new Heliboy(5300 + randomInt, 360);
        hb11 = new Heliboy(5700 + randomInt, 360);
        hb12 = new Heliboy(6000 + randomInt, 360);
        hb13 = new Heliboy(6300 + randomInt, 360);
        hb14 = new Heliboy(6700 + randomInt, 360);
        hb15 = new Heliboy(7000 + randomInt, 360);
        hb16 = new Heliboy(7200 + randomInt, 360);



        Thread thread = new Thread(this);
        thread.start();
    }



    private void loadMap(String filename) throws IOException {
        ArrayList lines = new ArrayList();
        int width = 0;
        int height = 0;

        BufferedReader reader = new BufferedReader(new FileReader(filename));
        while (true) {
            String line = reader.readLine();
            // no more lines to read
            if (line == null) {
                reader.close();
                break;
            }

            if (!line.startsWith("!")) {
                lines.add(line);
                width = Math.max(width, line.length());

            }
        }
        height = lines.size();

        for (int j = 0; j < 12; j++) {
            String line = (String) lines.get(j);
            for (int i = 0; i < width; i++) {

                if (i < line.length()) {
                    char ch = line.charAt(i);
                    Tile t = new Tile(i, j, Character.getNumericValue(ch));
                    tilearray.add(t);
                }

            }
        }

    }



    @Override
    public void run() {
        if (state == GameState.Running) {


            while (true) {  

                robot.update();
                if (robot.isJumped()) {
                    currentSprite = characterJumped;
                } else if (robot.isJumped() == false
                        && robot.isDucked() == false) {

                    currentSprite = anim.getImage();
                }

                ArrayList projectiles = robot.getProjectiles();
                for (int i = 0; i < projectiles.size(); i++) {
                    Projectile p = (Projectile) projectiles.get(i);
                    if (p.isVisible() == true) {
                        p.update();

                    } else {
                        projectiles.remove(i);
                    }
                }

                updateTiles();
                hb.update();
                hb2.update();
                hb3.update();
                hb4.update();
                hb5.update();
                hb6.update();
                hb7.update();
                hb8.update();
                hb9.update();
                hb10.update();
                hb11.update();
                hb12.update();
                hb13.update();
                hb14.update();
                hb15.update();
                hb16.update();
                bg1.update();
                bg2.update();
                animate();
                repaint();
                try {
                    Thread.sleep(17);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                if (rHealth == 0) {
                    state = GameState.Dead;                 
                    Sound.MAIN.stop();
                    //Sound.DIE.play();

                    sOver = new Button("Start Over");
                    this.add(sOver);
                    sOver.addActionListener(this);
                    sOver.setVisible(true);                 
                    revalidate();
                    repaint();
                }
                if (robot.getCenterY() > 500) {
                    state = GameState.Dead;
                    Sound.MAIN.stop();
                    //Sound.DIE.play();

                    sOver = new Button("Start Over");
                    this.add(sOver);
                    sOver.addActionListener(this);
                    sOver.setVisible(true);                 
                    revalidate();
                    repaint();

                }

                if (score == 5){
                    state = GameState.Win;
                    Sound.MAIN.stop();
                    //Sound.WIN.play();

                    next = new Button("Next Level");
                    this.add(next);
                    next.addActionListener(this);
                    next.setVisible(true);  
                    revalidate();
                    repaint();

                }
            }
        }
    }

    public void animate() {
        anim.update(10);
        hanim.update(50);
    }

    @Override
    public void update(Graphics g) {
        if (image == null) {
            image = createImage(this.getWidth(), this.getHeight());
            second = image.getGraphics();
        }

        second.setColor(getBackground());
        second.fillRect(0, 0, getWidth(), getHeight());
        second.setColor(getForeground());
        paint(second);

        g.drawImage(image, 0, 0, this);

    }



    @Override
    public void paint(Graphics g) {

        if (state == GameState.Running) {

            g.drawImage(background, bg1.getBgX(), bg1.getBgY(), this);
            g.drawImage(background, bg2.getBgX(), bg2.getBgY(), this);
            paintTiles(g);

            ArrayList projectiles = robot.getProjectiles();
            for (int i = 0; i < projectiles.size(); i++) {
                Projectile p = (Projectile) projectiles.get(i);
                g.setColor(Color.BLUE);
                g.fillRect(p.getX(), p.getY(), 10, 5);
            }

            g.drawImage(currentSprite, robot.getCenterX() - 61,
                    robot.getCenterY() - 63, this);
            g.drawImage(hanim.getImage(), hb.getCenterX() - 48,
                    hb.getCenterY() - 48, this);
            g.drawImage(hanim.getImage(), hb2.getCenterX() - 48,
                    hb2.getCenterY() - 48, this);
            g.drawImage(hanim.getImage(), hb3.getCenterX() - 48,
                    hb3.getCenterY() - 48, this);
            g.drawImage(hanim.getImage(), hb4.getCenterX() - 48,
                    hb4.getCenterY() - 48, this);
            g.drawImage(hanim.getImage(), hb5.getCenterX() - 48,
                    hb5.getCenterY() - 48, this);
            g.drawImage(hanim.getImage(), hb6.getCenterX() - 48,
                    hb6.getCenterY() - 48, this);
            g.drawImage(hanim.getImage(), hb7.getCenterX() - 48,
                    hb7.getCenterY() - 48, this);
            g.drawImage(hanim.getImage(), hb8.getCenterX() - 48,
                    hb8.getCenterY() - 48, this);
            g.drawImage(hanim.getImage(), hb9.getCenterX() - 48,
                    hb9.getCenterY() - 48, this);
            g.drawImage(hanim.getImage(), hb10.getCenterX() - 48,
                    hb10.getCenterY() - 48, this);
            g.drawImage(hanim.getImage(), hb11.getCenterX() - 48,
                    hb11.getCenterY() - 48, this);
            g.drawImage(hanim.getImage(), hb12.getCenterX() - 48,
                    hb12.getCenterY() - 48, this);
            g.drawImage(hanim.getImage(), hb13.getCenterX() - 48,
                    hb13.getCenterY() - 48, this);
            g.drawImage(hanim.getImage(), hb14.getCenterX() - 48,
                    hb14.getCenterY() - 48, this);
            g.drawImage(hanim.getImage(), hb15.getCenterX() - 48,
                    hb15.getCenterY() - 48, this);
            g.drawImage(hanim.getImage(), hb16.getCenterX() - 48,
                    hb16.getCenterY() - 48, this);

            g.setFont(font);
            g.setColor(Color.WHITE);
            g.drawString("Health: " + Integer.toString(rHealth), 5, 30);
            g.drawString("Score: " + Integer.toString(score), 650, 30);

        } else if (state == GameState.Dead) {

            //setLayout(new FlowLayout());


            g.setColor(Color.BLACK);
            g.fillRect(0, 0, 800, 480);
            g.setColor(Color.WHITE);
            g.drawString("You're Dead!", 300, 200);
            g.drawString("Score: " + score, 300, 250);

        }
        else if (state == GameState.Win) {
            g.setColor(Color.BLACK);
            g.fillRect(0, 0, 800, 480);
            g.setColor(Color.WHITE);
            g.drawString("You Beat this level!", 300, 200);
            g.drawString("Score: " + score, 300, 250);
            level++;

        }
    }

    private void updateTiles() {

        for (int i = 0; i < tilearray.size(); i++) {
            Tile t = (Tile) tilearray.get(i);
            t.update();
        }

    }

    private void paintTiles(Graphics g) {
        for (int i = 0; i < tilearray.size(); i++) {
            Tile t = (Tile) tilearray.get(i);
            g.drawImage(t.getTileImage(), t.getTileX(), t.getTileY(), this);
        }
    }

    @Override
    public void keyPressed(KeyEvent e) {

        switch (e.getKeyCode()) {
        case KeyEvent.VK_UP:
            break;

        case KeyEvent.VK_DOWN:
            currentSprite = characterDown;
            if (robot.isJumped() == false) {
                robot.setDucked(true);
                robot.setSpeedX(0);
            }
            break;

        case KeyEvent.VK_LEFT:
            robot.moveLeft();
            robot.setMovingLeft(true);
            break;

        case KeyEvent.VK_RIGHT:
            robot.moveRight();
            robot.setMovingRight(true);
            break;

        case KeyEvent.VK_SPACE:
            robot.jump();
            break;

        case KeyEvent.VK_CONTROL:
            if (robot.isDucked() == false && robot.isJumped() == false
                    && robot.isReadyToFire()) {
                robot.shoot();  
                robot.setReadyToFire(false);

            }
            break;

        }

    }

    @Override
    public void keyReleased(KeyEvent e) {
        switch (e.getKeyCode()) {
        case KeyEvent.VK_UP:
            break;

        case KeyEvent.VK_DOWN:
            currentSprite = anim.getImage();
            robot.setDucked(false);
            break;

        case KeyEvent.VK_LEFT:
            robot.stopLeft();
            break;

        case KeyEvent.VK_RIGHT:
            robot.stopRight();
            break;

        case KeyEvent.VK_SPACE:
            break;

        case KeyEvent.VK_CONTROL:
            robot.setReadyToFire(true);
            Sound.GUN.play();
            break;

        }

    }

    @Override
    public void keyTyped(KeyEvent e) {
        // TODO Auto-generated method stub

    }


    public static Background getBg1() {
        return bg1;
    }

    public static Background getBg2() {
        return bg2;
    }

    public static Robot getRobot() {
        return robot;
    }

    @Override
    public void actionPerformed(ActionEvent evt) {
        if (evt.getSource() == next)
            level ++;

        {


        }
        if (evt.getSource() == sOver)

            level = 1;      

        {

        }
    }


}

我想错误就在这里。在将sOver添加到小程序之前，必须初始化它。这样说吧：

sOver = new Button("Start Over");
this.add(sOver);

---

让我们看看它是否有效。

编辑您的帖子，以包含您看到的特定错误消息。说“有一个错误，帮帮我”就像我问你“我今天看到一只鸟，你能告诉我它是什么吗？”而没有显示图片。使用中所示的。这确实消除了错误，因此朝着正确的方向迈出了一步。但是，“重新开始”按钮仍然不可见。我移动了sOver=新按钮（“重新开始”）；本条增补（原）；sOver.addActionListener（本）；在g.drawString下方向下编码（“分数：+Score，300250）；线，认为它可能被涂过了，但它仍然不可见。您可以尝试添加行sOver.setVisible（true）；下面是addActionListener（本）；没有变化。我有“You's dead”字符串和最终分数，但没有任何按钮。通常，如果将按钮代码放入applet的init（）方法中。它将自动添加。但是在您的例子中，您在运行时添加了一个按钮，那么在将按钮添加到applet之后，应该调用revalidate（）和repaint（）方法。revalidate（）会将组件更新为组件层次结构，repaint（）会重新绘制整个框架。你太棒了，我非常感谢你的帮助。

this.add(sOver);
sOver = new Button("Start Over");

sOver = new Button("Start Over");
this.add(sOver);