Why doesn't Collections.copy increase the size of the destination?

Question

I'm using the following code:

List<Object> dest = new LinkedList<Object>();
Collections.copy(oldList, src);

When i execute the code, I get an exception:

java.lang.IndexOutOfBoundsException: Source does not fit in dest
    at java.util.Collections.copy(Collections.java:589)

I know how to fix that, but what i don't understand is:

When i add elements manually, the list would increase the capacity automaticly. Why can't Collections#copy do that?

Answer 1

As StinePike already said in https://stackoverflow.com/a/21986805 : That's how it is implemented. It is just a convenience method that you can use instead of a for-loop like

for (int i=0; i<src.size(); i++)
{
    dst.set(i, src.get(i));
}

Regarding your question about the automatic size increase: It sounds as if you are actually looking for something like Collection#addAll(Collection) - so in this case

dest.addAll(src);

Answer 2

Because this is how it is implemented. If you see the source code of this method you will see that

 if (srcSize > dest.size())
    throw new IndexOutOfBoundsException("Source does not fit in dest");

So if you want to implement autoincrement, Then write your own method.