ImmutablePair stolen from GitHub, stored here for convenience.

Pair.java

public class Pair<L,R> {

    private final L left;
    private final R right;

    public Pair(L left, R right) {

        this.left = left;
        this.right = right;
    }

    public L getLeft() {
        
        return left;
    }
    public R getRight() {

        return right;
    }

    @Override
    public int hashCode() {

        return left.hashCode() ^ right.hashCode();
    }

    @Override
    public boolean equals(Object o) {

        if (!(o instanceof Pair)) return false;
        Pair pairo = (Pair) o;
        return this.left.equals(pairo.getLeft()) &&
                this.right.equals(pairo.getRight());
    }

}