long startTime = System.currentTimeMillis();  

//一帧的绘制运算 消耗时间不同
...
      
/** 计算出更新本次帧所消耗的毫秒数 **/  
int diffTime = (int) (System.currentTimeMillis() - startTime);        
              
/** 确保每次更新时间为50帧 **/
//方式1 线程休眠时间不同的影响需要查一下，再决定用何种方式
try {
    Thread.sleep(TIME_IN_FRAME-diffTime);
} catch (InterruptedException e) {
    e.printStackTrace();
}
//方式2 用线程等待
while (diffTime <= TIME_IN_FRAME) {  
    diffTime = (int) (System.currentTimeMillis() - startTime);  
    //线程等待   
    Thread.yield();  
}

public void run( )
    /* Repeatedly: update, render, sleep so loop takes close
       to period ms */
    {
      long beforeTime, timeDiff, sleepTime;

      beforeTime = System.currentTimeMillis( );

      running = true;
      while(running) {
        gameUpdate( );
        gameRender( );
        paintScreen( );

        timeDiff = System.currentTimeMillis( ) - beforeTime;
        sleepTime = period - timeDiff;   // time left in this loop

        if (sleepTime <= 0)  // update/render took longer than period
          sleepTime = 5;    // sleep a bit anyway

        try {
          Thread.sleep(sleepTime);  // in ms
        }
        catch(InterruptedException ex){}

        beforeTime = System.currentTimeMillis( );
      }

      System.exit(0);
    } // end of run( )