LookaheadIterator

LookaheadIterator.java

import java.util.Iterator;

public class LookaheadIterator implements Iterator {

    private Iterator iter;
    private boolean hasLookahead;
    private Object lookahead;

    public LookaheadIterator(Iterator iter) {
        this.iter = iter;
        hasLookahead = false;
    }

    public boolean hasNext() {
        return hasLookahead || iter.hasNext();
    }

    public Object next() {
        if (hasLookahead) {
            hasLookahead = false;
            return lookahead;
        } else {
            return iter.next();
        }
    }

    public void remove() {
        throw new UnsupportedOperationException();
    }

    public Object peek() {
        if (!hasLookahead) {
            lookahead = iter.next();
            hasLookahead = true;
        }
        return lookahead;
    }
}