FilterIterator.java

/*
 * Copyright (c) 2012,2013 Big Switch Networks, Inc.
 *
 * Licensed under the Eclipse Public License, Version 1.0 (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.eclipse.org/legal/epl-v10.html
 *
 * 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.
 *
 * This file incorporates work covered by the following copyright and
 * permission notice:
 *
 *    Originally created by David Erickson, Stanford University 
 *
 *    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 org.sdnplatform.util;

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * An iterator that will filter values from an iterator and return only
 * those values that match the predicate.
 */
public abstract class FilterIterator<T> implements Iterator<T> {
    protected Iterator<T> subIterator;
    protected T next;

    /**
     * Construct a filter iterator from the given sub iterator
     * @param subIterator the sub iterator over which we'll filter
     */
    public FilterIterator(Iterator<T> subIterator) {
        super();
        this.subIterator = subIterator;
    }

    /**
     * Check whether the given value should be returned by the
     * filter
     * @param value the value to check
     * @return true if the value should be included
     */
    protected abstract boolean matches(T value);
    
    // ***********
    // Iterator<T>
    // ***********

    @Override
    public boolean hasNext() {
        if (next != null) return true;
        
        while (subIterator.hasNext()) {
            next = subIterator.next();
            if (matches(next))
                return true;
        }
        next = null;
        return false;
    }

    @Override
    public T next() {
        if (hasNext()) {
            T cur = next;
            next = null;
            return cur;
        }
        throw new NoSuchElementException();
    }

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

}