java - 如何从另一个类访问对象变量？

Question

我在网上查了一下，有些东西有帮助，但我仍然没有让这个东西发挥作用。我正在制作一个简单的乒乓球游戏，但我想要它，所以我的所有代码都已正确设置。所以我有一个针对player1 Racket 、电脑 Racket 、球、主屏幕以及比赛屏幕的类。 因此，例如，我的player1Paddle类将具有该桨的所有运动，计算机桨类(player2)将具有该桨的所有运动，依此类推。 但是，当涉及到对计算机桨的简单 AI 进行编码时(基本上从左到右跟随球)，我无法访问球的位置

if(player2Pong.position.x > ballPong.position.x)

它带来了一个错误。现在我已经实例化了球类并且它可以工作，但我基本上已经制作了另一个球，但运动不存在。以下是尝试提供帮助的部分代码。我知道有很多代码，而且可能有一些是不需要的。 在我的 playScreen 上我调用player2movement -

player2Pong.Player2Movement();

这是大部分的player2pong类。

 public class Player2Pong {
    public Vector2 position;    
    String textureLoc;
    Texture Player2Texture; 
    float stateTime;    
    Rectangle player2Bounds;    
    String movement;    
    int speed = 2;
    int playerXVector = 5;
    SpriteBatch batch;

    //PlayerPong playerpong;
    Player2Pong player2pong;

    Ball ballPong;

    public int paddle_player2_Width = 80;
    public int paddle_player2_Height = 10;

    //PlayerPong player;

    public Player2Pong(Vector2 position, Ball ball){

        Player2Texture = new Texture(Gdx.files.internal(("paddle_player2.png")));
        this.position = position;       

        player2Bounds = new Rectangle(position.x,position.y,paddle_player2_Width, paddle_player2_Height);
        //this.player2pong = player2pong;   
        this.ballPong = ball;

    }

    public void update(){       

    }

public void Player2Movement(){  

    player2pong = new Player2Pong(new Vector2(Gdx.graphics.getWidth() / 2, Gdx.graphics.getHeight() - (Gdx.graphics.getHeight()/8)), ballPong); 

        System.out.println(player2pong.position.x);              

        if(player2pong.position.x > ballPong.getPosition().x){
            System.out.println("right");
            player2pong.position.x -= playerXVector;
        }

         else  if(player2pong.position.x < ballPong.getPosition().x){
            System.out.println("right");
            player2pong.position.x += playerXVector;
        }

         if(player2pong.position.x > Gdx.graphics.getWidth() - player2pong.getPaddle_player2_Width()-5){
             player2pong.position.x -= playerXVector;
         }

         if(player2pong.getPosition().x < 3){
             player2pong.position.x += playerXVector;
         }       

    }


public void draw(SpriteBatch batch){

        batch.draw(Player2Texture, position.x, position.y, paddle_player2_Width, paddle_player2_Height);            
    }

这是 playScreen 类的大部分内容

  public class PlayScreenPong implements Screen{

    private static final Color WHITE = null;
    SpriteBatch batch;

    PlayerPong playerPong; 
    Player2Pong player2Pong;

    InputProcessor inputProcessor;  
    Game game;
    Ball ballPong;
    Texture paddle_player1, paddle_player2; 
    ArrayList<Ball> balls;  
    ArrayList<Player2Pong> player2;

    Iterator<Ball> ballsIterator;   
    Vector2 position;   
    ShapeRenderer borderSR, ballSR; 
    Sound sound;
    boolean rectangles = true;
    Stage PlayScreenStage;
    Label label;
    LabelStyle style;
    BitmapFont font;

    int playerXVector = 10;

    int player1Score = 0;
    int player2Score = 0;

    public PlayScreenPong(Game game){
        this.game = game;

    }

    @Override
    public void render(float delta) {
        Gdx.gl.glClearColor(0,0,0,0);
        Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);       

        playerPong.update();
        //player2Pong.update();

        borderSR.begin(ShapeType.Line);
        borderSR.rect(1, 1, Gdx.graphics.getWidth()-5, Gdx.graphics.getHeight()-4);
        borderSR.setColor(1,1,1,1);
        borderSR.end();
        batch.begin();

        ballsIterator = balls.iterator();
        while(ballsIterator.hasNext()){
            Ball cur = ballsIterator.next();    
            cur.update();
            cur.draw(batch);            
        }       
        batch.draw(playerPong.getPlayerTexture(), playerPong.getPosition().x, playerPong.getPosition().y, playerPong.paddle_player1_Width, playerPong.paddle_player1_Height);   
        player2Pong.draw(batch);

        //batch.draw(player2Pong.getPlayer2Texture(), player2Pong.getPosition().x, player2Pong.getPosition().y, player2Pong.paddle_player2_Width, player2Pong.paddle_player2_Height);
        batch.end();
        score();


        PlayScreenStage.act();
        PlayScreenStage.draw();

        if(rectangles == true){
            ballPong.drawRectangle();
        }       
        player2Pong.Player2Movement();

    }

    @Override
    public void show() {

        batch = new SpriteBatch();
        paddle_player1 = new Texture(Gdx.files.internal("paddle_player1.png"));
        paddle_player2 = new Texture(Gdx.files.internal("paddle_player2.png"));
        borderSR = new ShapeRenderer();     

        balls = new ArrayList<Ball>();
        player2 = new ArrayList<Player2Pong>();

        if(Gdx.files.local("paddle_player1.dat").exists()){
            try {
                playerPong = new PlayerPong(new Vector2(Gdx.graphics.getWidth() / 2, Gdx.graphics.getHeight() / 8), "paddle_player1.png");
                playerPong.setPosition(PlayerPong.readPlayer());
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
            System.out.println("File exists, reading file");

        }else{
            playerPong = new PlayerPong(new Vector2(Gdx.graphics.getWidth() / 2, Gdx.graphics.getHeight() / 8),"paddle_player1.png");
            try {
                PlayerPong.savePlayer(playerPong);
            } catch (IOException e) {
                e.printStackTrace();
            }
            System.out.println("Player doesnt exist, creating and saving player");                      
        }

//      player2Pong = new Player2Pong(new Vector2(Gdx.graphics.getWidth() / 2, Gdx.graphics.getHeight() - (Gdx.graphics.getHeight()/8)), playerPong);
//      player2.add(player2Pong);

        ballPong = new Ball(new Vector2(Gdx.graphics.getWidth()/2,Gdx.graphics.getHeight()/2), playerPong);
        balls.add(ballPong);        
    }

    public void score(){        

        PlayScreenStage = new Stage();
        font = new BitmapFont(Gdx.files.internal("font.fnt"), false);
        style = new LabelStyle(font, Color.WHITE);
        label = new Label("Player 1: " + player1Score + "  :  " + player2Score + " :Player 2", style);
        label.setPosition(Gdx.graphics.getWidth()/2 - label.getWidth()/2, Gdx.graphics.getHeight()/25);
        label.setFontScale((float) 0.8);

        PlayScreenStage.addActor(label);
        Gdx.input.setInputProcessor(PlayScreenStage);
        batch = new SpriteBatch();  
        //System.out.println(ballPong.getPosition().y);

        //-------------------------------------if someone scores
        if(ballPong.getPosition().y< 1){
            player2Score = player2Score +1;
            //oppositionScore +=1;
            System.out.println("goal");
            //ballPong.reset();
        }

        if(ballPong.getPosition().y > Gdx.graphics.getHeight()-1 -ballPong.getBallSizeY()){
            player1Score = player1Score + 1;
            //ballPong.reset();
        }

    }

正如我之前所说，它有点啰嗦，但我想做的就是对player2pong类中AI的运动、ball类中球的运动以及player类中玩家的运动进行排序，然后调用playscreen类中render或show方法中的方法。随意问任何问题。我知道这是一个简单的答案，但我是新的:(必须从某个地方开始

Answer 1

好吧，我的想法可能是错的，但值得一试。

首先，您不需要每次调用 PlayerMovement() 函数时都创建一个新的 Player2pong 对象，您已经有了一个:P

其次，您永远不会为 player2Pong 属性分配任何内容。因此，当您尝试对其调用 draw() 时，没有任何东西可以调用它!:P