com.complexible.common.collect.AbstractPeekingIterator.java Source code

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Here is the source code for com.complexible.common.collect.AbstractPeekingIterator.java

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/*
 * Copyright (c) 2005-2013 Clark & Parsia, LLC. <http://www.clarkparsia.com>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.complexible.common.collect;

import java.util.NoSuchElementException;

import com.google.common.collect.PeekingIterator;

/**
 * Abstract implementation of {@link PeekingIterator} interface.
 * 
 * @author Evren Sirin
 */
public abstract class AbstractPeekingIterator<T> implements PeekingIterator<T> {
    private T mNext = null;

    protected abstract T fetchNext();

    protected void clearNext() {
        mNext = null;
    }

    /**
     * @inheritDoc
     */
    @Override
    public T next() {
        T aResult = peek();
        mNext = null;
        return aResult;
    }

    /**
     * @inheritDoc
     */
    @Override
    public T peek() {
        if (mNext == null) {
            mNext = fetchNext();
        }
        if (mNext == null) {
            throw new NoSuchElementException();
        }
        return mNext;
    }

    /**
     * @inheritDoc
     */
    @Override
    public void remove() {
        throw new UnsupportedOperationException();
    }

    /**
     * @inheritDoc
     */
    @Override
    public boolean hasNext() {
        if (mNext == null) {
            mNext = fetchNext();
        }
        return mNext != null;
    }
}