Android DevArt1：假设当前Activity为A,如果这时用户打开一个新的Activity B,那么B的onResume和A的onPause哪个先执行呢？

public class AActivity extends AppCompatActivity { @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_a);
} public void goToBActivity(View view) {
startActivity(new Intent(this, BActivity.class));
} @Override
protected void onPause() {
super.onPause();
System.out.println("AActivity.onPause");
} @Override
protected void onStop() {
super.onStop();
System.out.println("AActivity.onStop");
}
}

public class BActivity extends AppCompatActivity { @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_b);
} @Override
protected void onStart() {
super.onStart();
System.out.println("BActivity.onStart");
} @Override
protected void onResume() {
super.onResume();
System.out.println("BActivity.onResume");
}
}

03-31 17:08:56.144 4861-4861/com.art.exploration I/System.out: AActivity.onPause
03-31 17:08:56.187 4861-4861/com.art.exploration I/System.out: BActivity.onStart
03-31 17:08:56.189 4861-4861/com.art.exploration I/System.out: BActivity.onResume
03-31 17:08:56.569 4861-4861/com.art.exploration I/System.out: AActivity.onStop

When activity B is launched in front of activity A, this callback will
be invoked on A. B will not be created until A's {@link #onPause} returns,
so be sure to not do anything lengthy here.