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The coolest XML library for Java around. Define typesafe views (projections) to xml. Use XPath to read and write XML. Bind XML to Java collections. Requires at least Java6, supports Java8 features and has no further runtime dependencies.

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/**
 *  Copyright 2015 Sven Ewald
 *
 *  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.xmlbeam.util;

import java.util.Iterator;

/**
 * A read only Iterator implementation that unions two other iterators.
 *
 * @author sven
 * @param  container type
 */
public class UnionIterator implements Iterator {

    private final Iterator first;
    private final Iterator second;

    /**
     * @param first
     * @param second
     */
    public UnionIterator(final Iterator first, final Iterator second) {
        if (first == null) {
            throw new NullPointerException("first iterator must not be null.");
        }
        if (second == null) {
            throw new NullPointerException("second iterator must not be null.");
        }
        if (first == second) {
            throw new NullPointerException("first and second iterators must not be the same.");
        }

        this.first = first;
        this.second = second;
    }

    @Override
    public boolean hasNext() {
        return first.hasNext() || second.hasNext();
    }

    @Override
    public T next() {
        return first.hasNext() ? first.next() : second.next();
    }

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

}