点击两次返回键程序退出

//连续两次返回退出程序
		private long exitTime = 0;  
		@Override  
		public boolean onKeyDown(int keyCode, KeyEvent event) {  
		    if(keyCode == KeyEvent.KEYCODE_BACK && event.getAction() == KeyEvent.ACTION_DOWN){                    
		    if((System.currentTimeMillis()-exitTime) > 2000){  
		        Toast.makeText(getApplicationContext(), "再按一次退出程序", Toast.LENGTH_SHORT).show();                                exitTime = System.currentTimeMillis();  
		    }  
		    else{  
		        finish();  
		        System.exit(0);  
		        }  
                  
		    return true;  
		    }  
		    return super.onKeyDown(keyCode, event);  
		}  //End of 连续两次返回退出程序

privatestatic Boolean isExit =false;  
    privatestatic Boolean hasTask =false;  
    Timer tExit =new Timer();  
    TimerTask task =new TimerTask() {  
           
        @Override  
        publicvoid run() {  
            isExit =false;  
            hasTask =true;  
        }  
    };  
  
  
publicboolean onKeyDown(int keyCode, KeyEvent event) {  
                // TODO Auto-generated method stub  
if(keyCode == KeyEvent.KEYCODE_BACK){  
//                        System.out.println("user back down");  
if(isExit ==false ) {  
                                isExit =true;  
                                Toast.makeText(this, "再按一次退出程序", Toast.LENGTH_SHORT).show();  
                                if(!hasTask) {  
                                        tExit.schedule(task, 2000);  
                                }} else {  
                                                                                }  
                                finish();  
                                System.exit(0);  
                        }  
                }                          
                returnfalse;  
        }