Java - allocation in enhanced for loop

Question

I have small problem in java with allocation of my object in "enhanced for loop". I tried something like this, which gives me later nullPointerException:

SomeClass tab[] = new SomeClass[100];
for( SomeClass x : tab){
  x = new SomeClass();
}

So... Earlier I code in C++ and It was possible to edit in any way (and sure also allocate memory) object, when just add & operator, like this:

SomeClass *tab = new SomeClass[100];
for( auto & x : tab){
  x = new SomeClass();
}

...and everything works well. But how is it in java? Is there any way to use this for loop when allocate some memory or not?

Answer 1

No, you cannot use an enhanced for loop to initialize the elements of an array. The declared variable, here x , is a separate variable that refers to the current element in the array. It's null here because you just declared the array. You are changing x to refer to a new SomeClass , but that doesn't affect the array at all.

0    | 1    | 2    | ...
-------------------------
|    |      |      | ...
v
null <--- x

After assignment to x:

0    | 1    | 2    | ...
-------------------------
|    |      |      | ...
v
null

x --> new SomeClass()

Java variables are different from C++ references in this behavior. Assigning a Java reference variable does not affect anything else that might refer to the same object.

You must use an array access expression, which requires an index. A standard for loop will work here.

SomeClass tab[] = new SomeClass[100];
for (int i = 0; i < tab.length; i++)
{
    tab[i] = new SomeClass();
}