com.jnape.palatable.lambda.iterators.ReversingIterator Maven / Gradle / Ivy

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package com.jnape.palatable.lambda.iterators;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.ListIterator;

public class ReversingIterator extends ImmutableIterator {
    private final Iterator     as;
    private final ListIterator reversingIterator;

    public ReversingIterator(Iterator as) {
        this.as = as;
        reversingIterator = new ArrayList().listIterator();
    }

    @Override
    public boolean hasNext() {
        return readyToReverse() ? reversingIterator.hasPrevious() : as.hasNext();
    }

    @Override
    public A next() {
        if (!readyToReverse())
            prepareForReversal();

        return reversingIterator.previous();
    }

    private void prepareForReversal() {
        while (as.hasNext())
            reversingIterator.add(as.next());
    }

    private boolean readyToReverse() {
        return reversingIterator.hasNext() || reversingIterator.hasPrevious();
    }
}