java returning a clone of an arraylist wrapped in collections.synchronizedlist

Question

I am wondering how I could produce a clone of my array in the following scenario:

private List<TestObject> testList = Collections.synchronizedList(new ArrayList<TestObject>());

....

public synchronized List<TestObject> getAllTestObjects(){
    return testList.clone();
    //I have tried casting to List<TestObject>
}

It is moaning about clone() being undefined for List. But I am not sure how best to get around it?

Any help would be greatly appreciated.

Boris the Spider · Accepted Answer · 2013-03-19 16:52:29Z

3

You need to use the constructor provided by ArrayList

public synchronized List<TestObject> getAllTestObjects(){
    return new ArrayList<TestObject>(testList);        
}

answered Mar 19, 2013 at 16:52

Boris the Spider

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4 Comments

ataulm Over a year ago

is the synchronized required here?

Boris the Spider Over a year ago

Yes because the copy constructor runs a loop over the given list. See my related answer here - that's for a Set but the same logic holds.

erdal.karaca Over a year ago

Ist it safe to just synchronize the method execution when copying the list? AFAIK, you should synchronize on the testList itself.

Boris the Spider Over a year ago

@erdal.karaca that depends entirely on your program logic and is a topic too broad for a comment.

OldCurmudgeon · Accepted Answer · 2013-03-19 16:59:33Z

0

This should work:

private static class TestObject {
}
private TestObject[] objects = new TestObject[10];
private List<TestObject> testList = 
  Collections.synchronizedList(new ArrayList<TestObject>(Arrays.asList(objects)));

answered Mar 19, 2013 at 16:59

OldCurmudgeon

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