線程變量不斷變化

Question

我有兩個線程通過這個相同的類BouncingObject運行。 BouncingObject只是反彈屏幕邊界。在某些時候，我想在主線程中重新定義這些屏幕邊界。但由於某種原因，它並不奏效。當我用alterBounceBoundaries方法改變屏幕邊界時，它改變了它們，但並不完全。使用方法和初始化值，邊界值在設定的邊界之間保持不同。爲什麼？。正如你所看到的，我在線程運行時打印出限制值，並且我可以看到orig_x，orig_y，lim_x，lim_y的值在已更改的值和已初始化的值之間切換。這些值是bounceobject檢測屏幕邊界的方式。

class BouncingObject extends D_Object implements Runnable 
{ 
    public int MAX_SPEED = 20; 
    public int MIN_SPEED = 10; 
    public volatile double orig_x = 0; 
    public volatile double orig_y = 0; 
    public volatile double lim_x = 0; 
    public volatile double lim_y = 0; 
    public String rand = "rand"; 

    BouncingObject(String nm,BufferedImage image, int x,int y, int w, int h, int ox, int oy, int spd){ 
     super(nm,image,x,y,w,h,ox,oy,spd); 
     orig_x = 0; 
     orig_y = 0; 
     lim_x = 603; 
     lim_y = 393; 
     Thread new_bounce_thread = new Thread(this); 
     new_bounce_thread.start(); 
    } 

    //run this code in it's own thread 
    public void run() { 
     while(true){ 
      //sleep for a short time to create a slower frame rate 
      try {Thread.sleep (20); } 
      catch (InterruptedException e){} 
      this.bounceObject(orig_x,orig_y,lim_x,lim_y,"rand"); 
      System.out.println("orig_x: "+orig_x); 
      System.out.println("orig_y: "+orig_y); 
      System.out.println("lim_x: "+lim_x); 
      System.out.println("lim_y: "+lim_y); 
     } 
    } 

public synchronized void alterBounceBoundaries(double origin_x, double origin_y, double limit_x, double limit_y, String rand_o_no){ 
     orig_x = origin_x; 
     orig_y = origin_y; 
     lim_x = limit_x; 
     lim_y = limit_y; 
     rand = rand_o_no; 
     System.out.println("Change Boundaries"); 
    } 

//used to determine when the bouncingobject has reached a little and needs to bounce 
public synchronized void bounceObject(double origin_x, double origin_y, double limit_x, double limit_y, String rand_o_no){ 
     if(obj_x > old_obj_x){ 
      old_obj_x = obj_x; 
.... 

Answer 1

如果你有兩個線程運行彈跳對象，你可能有兩個對象被彈回。我敢打賭，你只是在改變其中的一個限制。

基本上，當您想要更改限制時，請確保更改所有對象的限制。

另一種替代方法是設置限制static，以便它們由對象的所有實例共享。