public class MainActivity extends Activity {
  private String tag = "MainActivity";
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Log.i(tag, "onCreat");  //Activity被系统实例化之后触发
  }
  @Override
  protected void onStart() {
    super.onStart();
    Log.i(tag, "onStart()");   //onCreat或onRestart方法之后触发
  }

  @Override
  protected void onResume() {
    super.onResume();
    Log.i(tag, "onResume()");   //onStart之后触发
  }

  @Override
  protected void onPause() {
    super.onPause();
    Log.i(tag, "onStart()");   //使Activity处于暂停状态时触发
  }

  @Override
  protected void onStop() {
    super.onStop();
    Log.i(tag, "onStop()");    //Activity处于停止状态时触发
  }

  @Override
  protected void onRestart() {
    super.onRestart();
    Log.i(tag, "onRestart");   //从停止状态转变为运行状态时触发
 }

  @Override
  protected void onDestroy() {
    super.onDestroy();
    Log.i(tag, "onDestroy()");     //使Activity处于系统回收时触发
  }
}

如有不足，欢迎指出。

Activity生命周期