Get exception while using System.arraycopy for copy to ArrayList, gets: ArrayStoreException: null

Question

I have some trouble while trying to copy two arrays. Consider following simple code:

    ArrayList<Integer> t1 = new ArrayList<Integer>();
    Integer i1 = new Integer(1);
    Integer i2 = new Integer(2);
    t1.add(i1);
    t1.add(i2);

    ArrayList<Integer> t2 = new ArrayList<Integer>();
    System.arraycopy(t1, 0, t2, 0, t1.size());

Console shows: java.lang.ArrayStoreException: null . What can be wrong in this code, or how can I do it in different way. Sorry about may be easy question but I'm stuck on this for some hours and can't fix it.

Eric Galluzzo · Accepted Answer · 2013-02-18 14:37:53Z

12

System.arraycopy expects arrays (e.g. Integer[]) as the array parameters, not ArrayLists.

If you wish to make a copy of a list like this, just do the following:

List<Integer> t2 = new ArrayList<Integer>(t1);

answered Feb 18, 2013 at 14:37

Eric Galluzzo

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Subhrajyoti Majumder · Accepted Answer · 2013-02-18 14:40:17Z

3

You need Collections#copy

Collections.copy(t1,t2);

It will copies all of the elements from t1 list into t2.

answered Feb 18, 2013 at 14:40

Subhrajyoti Majumder

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Comments

el.nicko · Accepted Answer · 2015-02-03 10:49:39Z

1

In case anybody wants to add just a portion of the second ArrayList, one might do it like this:

ArrayList<Integer> t1 = new ArrayList<Integer>();
Integer i1 = new Integer(1);
Integer i2 = new Integer(2);
Integer i3 = new Integer(3);
t1.add(i1);
t1.add(i2);
t1.add(i3);

ArrayList<Integer> t2 = new ArrayList<Integer>();

/*
 * will add only last two integers
 * as it creates a sub list from index 1 (incl.)
 * to index 3 (excl.)
 */
t2.addAll(t1.subList(1, 3));

System.out.println(t2.size()); // prints 2
System.out.println(t2.get(0)); // prints 2
System.out.println(t2.get(1)); // prints 3

answered Feb 3, 2015 at 10:49

el.nicko

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Javier · Accepted Answer · 2013-02-18 14:45:19Z

0

easier:

ArrayList<Integer> t2 = new ArrayList<Integer>(t1);

or if the t2 has already been created

t2.clear();
t2.addAll(t1);

answered Feb 18, 2013 at 14:45

Javier

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