Request for binary search using functions

[Julian Hyde]

On Dec 12, 2012, at 1:49 AM, Peter Levart <peter.levart at gmail.com> wrote:

> Like that?

Almost what I was after, but not quite. I was looking for something that could implement any kind of abstract list, not just one based on an array.

The problem is that AbstractList has two abstract functions, and a lambda only has one. But I find that whenever I create an AbstractList its size is fixed at create time, and this is true here also. So, let's define a library method that takes a size and a gettable and returns a list:

    interface Gettable<T> {
        T get(int i);
    }

    private static abstract class RandomAccessAbstractList<E>
        extends AbstractList<E>
        implements RandomAccess {}

    public static <T> List<T> list(final int size, final Gettable<T> gettable) {
        return new RandomAccessAbstractList<T>() {
            public T get(int index) {
                return gettable.get(index);
            }

            public int size() {
                return size;
            }
        };
    }

Assuming that the list() method is part of a standard library (anyone on this list feel like adding it?!), the binary search problem can now be solved in one line:

        SimpleDateFormat[] array;
        String seek;
        return Collections.binarySearch(list(array.length, (i) -> array[i].toPattern()), seek);

Julian