編譯器錯誤不兼容類型：java.lang對象無法轉換

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我有一個項目在我的（OOP）類中。這是任務：改變反彈方法，將球放置在屏幕上半部分的任意位置。編譯器錯誤不兼容類型：java.lang對象無法轉換

這是我應得的

import java.awt.Color; 
import java.util.ArrayList;     
import java.util.Random; 
/** 
* Class BallDemo - a short demonstration showing animation with the 
* Canvas class. 
* 
* @author Michael Kölling and David J. Barnes 
* @version 2016.02.29 
*/ 

public class BallDemo 
{ 
    private Canvas myCanvas; 
    private ArrayList ball; 
    private BouncingBall bounceBall; 
    private Random randomGenerator; 

    /** 
     * Create a BallDemo object. Creates a fresh canvas and makes it visible. 
     */ 
    public BallDemo() 
    { 
     myCanvas = new Canvas("Ball Demo", 600, 500); 
    } 

    /** 
     * Simulate two bouncing balls 
     */ 
    public void bounce() 
    { 
     int ground = 400; // position of the ground line 
     ball = new ArrayList(); 
     randomGenerator = new Random(); 

     myCanvas.setVisible(true); 
     myCanvas.erase(); 

     // draw the ground 
     myCanvas.drawLine(50, ground, 550, ground); 

     // create and show the balls 
     BouncingBall ball1 = new BouncingBall(position(),position(),16,Color.BLUE,ground,myCanvas); 
     ball1.draw(); 
     BouncingBall ball2 = new BouncingBall(position(),position(),20,Color.RED,ground,myCanvas); 
     ball2.draw(); 
     BouncingBall ball3 = new BouncingBall(position(),position(),20,Color.BLACK,ground,myCanvas); 
     ball3.draw(); 
     //Add balls to ArrayList 
     ball.add(ball1); 
     ball.add(ball2); 
     ball.add(ball3); 

     This is where I get the error: 

     // make them bounce 
     boolean finished = false; 
     while (!finished) { 
      myCanvas.wait(50);   // small delay 
      for(int i = 0; i < ball.size(); i++) { 
       **bounceBall = ball.get(i);**   
       bounceBall.move(); 

      // stop once ball has travelled a certain distance on x axis 
      if(bounceBall.getXPosition() >= 550) { 
       finished = true; 
      } 
     } 
    } 
} 

    /** 
    * Randomly generates the position 
    * Pick the number between 0 to 200 
    */ 

    public int position() { 
     return randomGenerator.nextInt(200); 
    } 
}

這是由一個專家級的程序員幫助，但我仍然得到編譯器錯誤，這是bounceBall = ball.get(i);主要圍繞第（i）左右。

來源

2016-12-04 Polska711

共享編譯錯誤 – Shashank

發生這種情況是因爲您有一個Object類型的對象列表，而不是BouncingBall對象列表，因此編譯器無法將對象轉換爲BouncingBall。如果您使用的Java版本> = 1.5，使用類型列表： ArrayList<BouncingBall> ball，或投對象BouncingBall：bounceBall = (BouncingBall)ball.get(i);

來源

2016-12-04 16:32:10 Sergi

變化

ArrayList ball;

到

ArrayList<BouncingBall> ball;

將解決你的問題。

ArrayList默認爲ArrayList < Object>。因此，你會得到錯誤在線bounceBall = ball.get（i）;因爲您正嘗試將Object分配給BouncingBall

來源

2016-12-04 16:35:25 Shashank

編譯器錯誤不兼容類型：java.lang對象無法轉換

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