为什么MediaPlayer类没有使用new关键字实例化

Question

I am looking at some tutorials for Android development and I saw the case below

MediaPlayer mp = MediaPlayer.create(this, R.id.song)

My question is the following: Why isn't there a "new" keyword involved when creating a new MediaPlayer object? I thought that new has to be used anytime you create a instance of class

So what if I do

MediaPlayer mp = new MediaPlayer(); 
mp.create(this, R.id.song);

is this wrong?

Answer 1

My question is the following: Why isn't there a "new" keyword involved when creating a new MediaPlayer object?

Well you're calling a static method which will (presumably) create a new instance.

Maybe that method calls the constructor directly - or maybe it creates an instance of some subclass. Or maybe it returns a reference to an existing instance instead.

That's the nice thing about factory methods - they get to hide their implementation details :)

Answer 2

This is a "factory"-function. Internally it calls new MediaPlayer() , you just do not see it from outside of the class.

Answer 3

You are actually allowed to call new on a MediaPlayer.

The following is taken from http://developer.android.com/reference/android/media/MediaPlayer.html

When a MediaPlayer object is just created using new or after reset() is called, it is in the Idle state [...] Furthermore, the MediaPlayer objects created using new is in the Idle state, while those created with one of the overloaded convenient create methods are NOT in the Idle state. In fact, the objects are in the Prepared state if the creation using create method is successful.

Basically using new vs the static method just changes what state your MediaPlayer is in. If you new one, then you'll have to initialize it with setDataSource() and prepare it with onPrepare(). Where as your all ready to go with the static helper.