How can I initialize an array with an enhanced for-loop?

Question

I was optimizing an application and wanted to change my for loops to enhanced loops:

From:

for (int m = 1;m < MAX_BEREN;m++)
{           
    Wasberen[m] = new Wasbeer();       
    Wasberen[m].YYY = r.nextInt(SchermY - 28);
}

to:

for (Wasbeer a : Wasberen)
{
    if (a!=null)
    {
       a = new Wasbeer();
       a.YYY = r.nextInt(SchermY - 28);
    }
}

I get a NullPointerException, because it probably doesnt know how much 'beren' can be in the array, but I'm not sure how to manage the same as the loop above (MAX_BEREN = 11).

Brandon E Taylor · Accepted Answer · 2011-09-01 18:29:18Z

1

If the array reference ('Wasberen' in this case) in an enhanced for statement is null, then a NullPointerException will result when the statement is executed.

edited Sep 1, 2011 at 18:29

answered Sep 1, 2011 at 18:22

Brandon E Taylor

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2 Comments

Mars Over a year ago

So I initialize with the 'for' and iterate in later stages with the enhanced loop? Because the 'wasberen' already exist after init

Brandon E Taylor Over a year ago

The NullPointerException could be thrown, given your snippet, from the Wasbeer no-arg constructor or if 'r' is a null reference as well. The stack trace for the exception should identify the culprit.

kabuko · Accepted Answer · 2011-09-01 18:21:39Z

1

For initializing arrays, you should stick to the syntax you had before.

answered Sep 1, 2011 at 18:21

kabuko

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1 Comment

bitle Over a year ago

a[i] = new Object(); is not equal to Object b = a[i]; b = new Object();

Paŭlo Ebermann · Accepted Answer · 2011-09-02 16:42:00Z

1

You can't use the enhanced for-loop in Java to fill an array. (I'm assuming your Wasberen array was already created before - if not, this will get you a NullPointerException in both variants.)

Your code (simplified)

for (Wasbeer a : Wasberen)
{
    a = ...;
}

is equivalent to

for (int i = 0; i < Wasberen.length; i++)
{
    Wasbeer a = Wasberen[i];
    a = ...;
}

This assignment will change the local variable a, but will have no effect on the contents of the array.

answered Sep 2, 2011 at 16:42

Paŭlo Ebermann

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