Android: Issue during Arraylist declaration

Question

If I declare Arraylist like this-

private ArrayList<Integer[]> nodeList;

then, while adding array into it, getting NullPointerException

But, if I change it to-

private ArrayList<Integer[]> nodeList= new ArrayList<Integer[]>();

-it works fine.

Why the first one fails!

As you state, in first case you declare it only, but its initial value is null. — harism
– harism, Commented Nov 9, 2011 at 15:41
@Avisek stackoverflow.com/questions/8065763/… :) no offense but you should read some books about programming in java — Selvin
– Selvin, Commented Nov 9, 2011 at 15:46
ya am a noob & am clarifying while trying exercises. Actually, its much confusive to switch to JAVA from PHP — Avisek Chakraborty
– Avisek Chakraborty, Commented Nov 9, 2011 at 16:29

amit · Accepted Answer · 2011-11-09 15:46:00Z

3

The first only declares a variable, but does not create the actual object. only when you use new, you actually create the object.

In java unlike C++, declaring a variable does not allocate a local variable of it. To actually create the object, you need to explicitly create it [in your example: by using the new keyword].
(*)Note that this is only true to reference types objects, and java primitives are created with declaration.

edited Nov 9, 2011 at 15:46

answered Nov 9, 2011 at 15:40

amit

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