fragment有什么优势

public class MainActivity extends Activity

{



    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        Button b = (Button)findViewById(R.id.bt);

        b.setOnClickListener(new View.OnClickListener() {

            @Override

            public void onClick(View view) {

                setContentView(R.layout.ooo);

            }

        });

    }

}