creating array without declaring the size - java

Question

i've digging around about the same issue but i couldn't find the same as i had

i want to create an array without declaring the size because i don't know how it will be !

to clear the issue i'd like to give you the code that i'm looking up for

public class t
{
 private int x[];
 private int counter=0;
 public void add(int num)
 {
   this.x[this.counter] = num;
   this.counter++;
 }
}

as you see the user could use the add function to add element to the array 10000 times or only once so it's unknown size

Yea, use ArrayList; it's like an array that can grow dynamically, you can get by index, put by index, put at end.... it's convenient. — Shark
– Shark, Commented Aug 16, 2012 at 15:28

Martin Erhardt · Accepted Answer · 2012-08-16 15:25:18Z

13

Using Java.util.ArrayList or LinkedList is the usual way of doing this. With arrays that's not possible as I know.

Example:

List<Float> unindexedVectors = new ArrayList<Float>();

unindexedVectors.add(2.22f);

unindexedVectors.get(2);

answered Aug 16, 2012 at 15:25

Martin Erhardt

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Kevin Mangold · Accepted Answer · 2012-08-16 15:25:25Z

9

You might be looking for a List? Either LinkedList or ArrayList are good classes to take a look at. You can then call toArray() to get the list as an array.

answered Aug 16, 2012 at 15:25

Kevin Mangold

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Comments

user377628 · Accepted Answer · 2012-08-16 15:31:38Z

3

As others have said, use ArrayList. Here's how:

public class t
{
 private List<Integer> x = new ArrayList<Integer>();

 public void add(int num)
 {
   this.x.add(num);
 }
}

As you can see, your add method just calls the ArrayList's add method. This is only useful if your variable is private (which it is).

answered Aug 16, 2012 at 15:31

user377628

2 Comments

Kevin Mangold Over a year ago

What is the purpose of wrapping the ArrayList in another class?

user377628 Over a year ago

If this is the entire class, then there is no purpose. But I wanted to show the OP how to use ArrayLists with his own code.

GONE · Accepted Answer · 2013-08-29 17:34:20Z

3

Once the array size is fixed while running the program ,it's size can't be changed further. So better go for ArrayList while dealing with dynamic arrays.

answered Aug 29, 2013 at 17:34

GONE

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user2720864 · Accepted Answer · 2014-08-28 09:40:50Z

3

How about this

    private Object element[] = new Object[] {};

answered Aug 28, 2014 at 9:40

user2720864

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1 Comment

shirjai Over a year ago

this basically says an array of size 0 . I doubt this would work.

linuxuser27 · Accepted Answer · 2012-08-16 15:26:12Z

1

I think what you really want is an ArrayList or Vector. Arrays in Java are not like those in Javascript.

answered Aug 16, 2012 at 15:26

linuxuser27

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