How to copy a java.util.List into another java.util.List

java collections copy
Mono Jamoon picture Mono Jamoon · Jan 14, 2013 · Viewed 252.6k times · Source

I have a List<SomeBean> that is populated from a Web Service. I want to copy/clone the contents of that list into an empty list of the same type. A Google search for copying a list suggested me to use Collections.copy() method. In all the examples I saw, the destination list was supposed to contain the exact number of items for the copying to take place.

As the list I am using is populated through a web service and it contains hundreds of objects, I cannot use the above technique. Or I am using it wrong??!! Anyways, to make it work, I tried to do something like this, but I still got an IndexOutOfBoundsException.

List<SomeBean> wsList = app.allInOne(template);

List<SomeBean> wsListCopy=new ArrayList<SomeBean>(wsList.size());   
Collections.copy(wsListCopy,wsList);
System.out.println(wsListCopy.size());

I tried to use the wsListCopy=wsList.subList(0, wsList.size()) but I got a ConcurrentAccessException later in the code. Hit and trial. :)

Anyways, my question is simple, how can I copy the entire content of my list into another List? Not through iteration, of course.

Answer

fge picture fge · Jan 14, 2013

Just use this:

List<SomeBean> newList = new ArrayList<SomeBean>(otherList);

Note: still not thread safe, if you modify otherList from another thread, then you may want to make that otherList (and even newList) a CopyOnWriteArrayList, for instance -- or use a lock primitive, such as ReentrantReadWriteLock to serialize read/write access to whatever lists are concurrently accessed.

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