The correct way to create and initialize objects in android

Question

I have several packages in my Android project containing several classes. When I want to create an object of a certain class in user interface activity, I used the method of creating a private object and initialized it to the method onCreate()where the user interface actions are in a separate package.

private SomeClass someClass = new SomeClass();

onCreate(Bundle savedInstanceState) {
   // Activity
}

I noticed that my senior programmers use a different method to declare an object before onCreate()and initialize it when the object is needed. What is the difference and suggest me the best way? I want me to be right if I am doing something wrong.

Answer 1

, , . . , . :

• . , null, , .
• , . . :
  String LOG_TAG = MyActivity.class.getSimpleName();
• . , , , , . :

, .

Answer 2

- . nullpointer, . . , String:

String mystring;
//in some functions deep inside code
mystring = "hello world";//works great with string

:

StringBuffer mystring;
//in some functions deep inside code
mystring.append("hello world");

mystring = new StringBuffer(); ,.append nullpointer, , , . , . arrayList .

Answer 3

, , / onCreate, . ( )

outside / , (onCreate), , , , , if(var != null), NullPointeException. ( Gloabal)

, , , , var

, MediaPlayer, Activity , , onCreate, onResume, onStop onDestroy, :

• MediaPleyr (onCreate)

• , (onResume), MediaPlayer

• Activity MediaPlayer (onPause)

• , , "IllegalState" (onDestroy)

* (onPreparedListener, onCompletionListener,...), .