B T B T - 4 months ago 67x
Java Question

How can I slice an ArrayList out of an ArrayList in Java?

How do I get an array slice of an

in Java? Specifically I want to do something like this:

ArrayList<Integer> inputA = input.subList(0, input.size()/2);
// where 'input' is a prepouplated ArrayList<Integer>

So I expected this to work, but Java returns a
- so it's incompatible. And when I try to cast it, Java won't let me. I need an
- what can I do?


In Java, it is good practice to use interface types rather than concrete classes in APIs.

Your problem is that you are using ArrayList (probably in lots of places) where you should really be using List. As a result you created problems for yourself with an unnecessary constraint that the list is an ArrayList.

This is what your code should look like:

List input = new ArrayList(...);

public void doSomething(List input) {
   List inputA = input.subList(0, input.size()/2);


Your proposed "solution" to the problem was/is this:

new ArrayList(input.subList(0, input.size()/2))

That works by making a copy of the sublist. It is not a slice in the normal sense. Furthermore, if the sublist is big, then making the copy will be expensive.