跳转（第一次进入显示欢迎界面，再次进入不显示）

//handler

Handler handler=new Handler(){
		public void handleMessage(android.os.Message msg) {
			if(msg.what==1)
			{
				timer.cancel();
				Intent intent=new Intent(MainActivity.this, MainActivity2.class);
				startActivity(intent);
				edit.putBoolean("tiao", true);
				edit.commit();
			}
			else if(msg.what==2)
			{
				time.setText(index+"");
			}
			
		};
		
	};
    private TextView time;
    int index=4;
	private Timer timer;
	private SharedPreferences sp;
	private Editor edit;
	@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        time = (TextView) findViewById(R.id.hy);

//SharedPreferences

       sp = getSharedPreferences("mydata", MODE_PRIVATE);
        edit = sp.edit();
        boolean boolean1 = sp.getBoolean("tiao", false);
        if(boolean1)
        {
        	Intent intent=new Intent(MainActivity.this, MainActivity2.class);
			startActivity(intent);
        	finish();
        }
        else
        {
        timer = new Timer(true);
        timer.schedule(new TimerTask() {
			
			@Override
			public void run() {
				index--;
				if(index<=0)
				{
					handler.sendEmptyMessage(1);
				}
				else{
					handler.sendEmptyMessage(2);
				}
				
			}
		}, 0, 1000);
        }
    }