我如何在與之無關的另一類中訪問一個項目的變量？

Question

我是java的新手，並且我已經搜索了很長時間。 如何在Player類中訪問項目的b變量？（我發布的鱈魚是我完整程序的一部分，因此請不要介意是否看到以下代碼中未聲明的方法或變量）

import java.util.Random;
public abstract class Player {
 private int x, y;
 private String name;
 private int pNumber;
 private int mLine;
 private int tLine;
 private boolean possession;
 private int c;
 private int f = 0;
 private int i = 0;


 public int getPlx() {
  return x;
 }
 public void setPlx(int x) {
  this.x = x;
 }
 public int getPly() {
  return y;
 }
 public void setPly(int y) {
  this.y = y;
 }
 public String getPName() {
  return name;
 }
 public void setPName(String name) {
  this.name = name;
 }
 public int getPNum() {
  return pNumber;
 }
 public void setPNum(int pNumber) {
  this.pNumber = pNumber;
 }
 public int getMLine() {
  return mLine;
 }
 public void setMLine(int mLine) {
  this.mLine = mLine;
 }
 public int getLine() {
  return tLine;
 }
 public void setTLine(int tLine) {
  this.tLine = tLine;
 }
 public boolean getPos() {
  return possession;
 }
 public void setPos(boolean possession) {
  this.possession = possession;
 }

 private Random rand = new Random();

 public void Move() { //me8odos metakinisis
  c = rand.nextInt(2);
  if (c == 0) {
   y++;
  } else {
   y--;
  }
 }
 public void Pass() {
  if (this.possession == true) {
   c = rand.nextInt(10);
   while ((f == 0) && (i < 10)) {
    if (main.barcelona.get(i).name == this.name) {}
   }
  }
 }
 public abstract void SpecialMove();
}

public class Ball {
 private int x, y;
 private Player formerP = null;
 private Player currentP = null;

 public Ball(int x, int y, Player formerP, Player currentP) {
  this.x = x;
  this.y = y;
  this.formerP = formerP;
  this.currentP = currentP;
 }

 public int getBX() {
  return x;
 }
 public void setBX(int x) {
  this.x = x;
 }
 public int getBY() {
  return y;
 }
 public void setBY(int y) {
  this.y = y;
 }

 void Assign(Player playerP) {
  int px = playerP.getPlx();
  if (this.currentP == null) {
   if (((this.x - px <= 1) || (px - this.x) <= 1) 
       && ((this.x - px <= 1) || (px - this.x) = 1)) {
    this.currentP = playerP;
    this.formerP.possession = false;
    playerP.possession = true;

    if (this.currentP.team == this.formerP.team) {
     int pass = this.currentP.getPasses();
     pass++;
     this.currentP.setPasses(pass);
    } else {
     int mistake = this.currentP.getMistakes();
     mistake++;
     this.currentP.setMistakes(mistake);
    }
   }
  }
  this.formerP = this.currentP;
  this.currentP = null;
  this.formerP = null;
 }
}

Answer 1

如果您不想在Player類中實例化Ball類， 並且想確保所有玩家都在玩一個唯一的球，請考慮將Ball變成Singleton 。

在軟件工程中，單例模式是一種設計模式，用於將類的實例化限制為一個對象。 當僅需要一個對象來協調整個系統中的動作時，這將很有用。

public class Ball {
    private static Ball singletonBall;

    private int x;
    private int y;
    private Player formerP;
    private Player currentP;


    public static Ball getSingletonBall() {
        if(singletonBall == null){
            singletonBall = new Ball();
        }
        return singletonBall;
    }

    public int getX() {
        return x;
    }


    public void setX(int x) {
        this.x = x;
    }


    public int getY() {
        return y;
    }


    public void setY(int y) {
        this.y = y;
    }


    public Player getFormerP() {
        return formerP;
    }


    public void setFormerP(Player formerP) {
        this.formerP = formerP;
    }


    public Player getCurrentP() {
        return currentP;
    }


    public void setCurrentP(Player currentP) {
        this.currentP = currentP;
    }
}

Answer 2

如果在Player內部需要經常使用的東西在Player對象（或子對象）的整個生命周期中都不會改變，那么您最好將其通過Player傳遞給局部變量構造函數。

假設項目B是Ball，並且您擁有Ball類。

因此，在播放器（或子播放器）中聲明要訪問的對象：

class Player {
    Ball ball;

    public Player(Ball ball) {
       this.ball = ball;
    }

或者，如果只是不經常使用的東西，或者有價值的東西會改變（更可能是球），則可以創建一種方法來執行Player對象上所需的操作。

class Player {
.
.
.
.
.
    public void dribble(Ball ball) {
    // do something with the ball
        ball.setPosition(10, 20);
        ball.update();
    }
}

然后，任何實例化的Player都可以訪問該方法。

public static void main(String[] args) {
    Player player = new Player();
    Ball ball = new Ball();
    player.dribble(ball);
} 

Answer 3

嘗試BallClassName.getX（）; 您可能必須使getX靜態