Empty Array

[Jamie Stokely]

My instructor wants me to write a program that will process an array of integers that will be of arbitrary size, with arbitrary values. He will then fill the array when hes grading my program. The program then does some other procedures which i won't get into now. I've been trying to add an empty array that takes input from the user that will give the array its size, and the values of its elements. However, whenever i try to declare an empty array i get an "array dimension missing" error. Little help?

[Paul Clapham]

You didn't post any code, which is unfortunate because you were asking about code that you wrote.

So I'm going to guess that you wrote "int array[] = new int[]" which doesn't say how many entries you want to put in the array. If that's the case, then say how many entries you want in the array. You do have other places where you've declared arrays to compare to, don't you? And if my guess was wrong, let's have a look at the code you're asking about.

And, welcome to the Ranch!

[Nitish Bangera]

Take a look at the Collection framework provided by Java. If you want some more out of it, you can look into Google's collection framework Guava.

[Campbell Ritchie]

You might find array initialisers useful

/*
 * If you declare and initialise together, you can miss out new int[]
 */
int[] numbers = {};
numbers = new int[0];

public void foo()
{
   /*
    * Re-assigned, not declared, so this time the new int[] bit
    * is required. This statement needs to be inside a method.
    */
   numbers = new int[]{1, 2, 3, 4};
}

public int[] getNumbers()
{
   return noResult ? new int[]{} : numbers;
}

As long as you declare the boolean called noResult appropriately, I think all that code will compile.

[Jamie Stokely]

My bad for not posting my own code. Resolved this issue myself. Regardless, thank you for the help.

[Rob Spoor]

Campbell Ritchie wrote:

new int[]{}

Why not just write new int[0]? It does the same thing but is shorter to write and easier to read.

[Campbell Ritchie]

I was trying to show all possibilities. Agree you would usually write new int[0].

[Nitish Bangera]

Campbell Ritchie wrote:You might find array initialisers useful

/*
 * If you declare and initialise together, you can miss out new int[]
 */
int[] numbers = {};
numbers = new int[0];

public void foo()
{
   /*
    * Re-assigned, not declared, so this time the new int[] bit
    * is required. This statement needs to be inside a method.
    */
   numbers = new int[]{1, 2, 3, 4};
}

public int[] getNumbers()
{
   return noResult ? new int[]{} : numbers;
}

As long as you declare the boolean called noResult appropriately, I think all that code will compile.

Don't you think using Collections would be better compared to making different array objects and then some of these object won't have a reference and would be garbage collected?

[Winston Gutkowski]

Nitish Bangera wrote:Don't you think using Collections would be better compared to making different array objects and then some of these object won't have a reference and would be garbage collected?

I agree that using collections is usually better, but in this case it appears that Jamie was told to use arrays. I'm also not quite sure where the garbage-collection comes in; an array will be garbage-collected just the same as a List - when it goes out of scope.

Winston

[Nitish Bangera]

numbers = new int[0];  
  
public void foo()  
{  
   /* 
    * Re-assigned, not declared, so this time the new int[] bit 
    * is required. This statement needs to be inside a method. 
    */  
   numbers = new int[]{1, 2, 3, 4};  
} 

What would happen to the original new int[0] when new int[] {1,2,3,4} is assigned to numbers? Out of scope is a different thing. Also, it would be a negligible thing in short programs.

[Henry Wong]

Nitish Bangera wrote:

numbers = new int[0];  
  
public void foo()  
{  
   /* 
    * Re-assigned, not declared, so this time the new int[] bit 
    * is required. This statement needs to be inside a method. 
    */  
   numbers = new int[]{1, 2, 3, 4};  
} 

What would happen to the original new int[0] when new int[] {1,2,3,4} is assigned to numbers? Out of scope is a different thing. Also, it would be a negligible thing in short programs.

Array references behaves just like any other object references -- arrays are objects after all. The array reference will simply refer to the newly assigned array. And if the old array is no longer reachable, it will be eligible for garbage collection.

Henry

[Winston Gutkowski]

Nitish Bangera wrote:What would happen to the original new int[0] when new int[] {1,2,3,4} is assigned to numbers?

An array is an object, just like any other, so it behaves exactly as it would if it was:
List<Integer> numbers = new List<Integer>();
...
numbers = Arrays.asList(1, 2, 3, 4);
or some other code that reassigns the variable.

Out of scope is a different thing.

I realise that. I'm afraid it's you who wasn't specific.

Winston

[Nitish Bangera]

Well that's exactly my point about the array object being garbage collected. I guess i wasn't specific and clear about it.

[Winston Gutkowski]

Nitish Bangera wrote:Well that's exactly my point about the array object being garbage collected. I guess i wasn't specific and clear about it.

So you do understand that there's absolutely no difference between the collectability of an array, and that of a List or any other collection?
What I think you might be thinking of is the collectibility of its elements: If you remove() an element from a List, it is generally available for collection, unless referenced anywhere else; but an array has no such method so it doesn't apply. You can, of course, null out an element, which will have the same effect.

Winston