MediaPlayer mediaPlayer 做什么...？ 在 java android

Question

import android.media.MediaPlayer;

public class Mainactivity extends AppCompatActivity{
    MediaPlayer mediaPlayer;

    public void play(View view){
        mediaPlayer.start();

Does ' MediaPlayer mediaPlayer; ' same as MediaPlayer mediaPlayer = New MediaPlayer(); ? If not, what does ' MediaPlayer mediaPlayer; ' do?

Answer 1

No, it's not the same.

MediaPlayer mediaPlayer;
mediaPlayer = new MediaPlayer();

would be the same as MediaPlayer mediaPlayer = new MediaPlayer();

The MediaPlayer mediaPlayer; is a declaration of this variable. It lets you instantiate it (create an object) at a different time than the declaration of this variable - for example in a constructor or a method.