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/*
 * Copyright 2002-2018 the original author or authors.
 *
 * 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
 *
 *      https://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.springframework.util;

import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.NoSuchElementException;
import java.util.Set;

/**
 * Composite iterator that combines multiple other iterators,
 * as registered via {@link #add(Iterator)}.
 *
 * 

This implementation maintains a linked set of iterators * which are invoked in sequence until all iterators are exhausted. * * @author Erwin Vervaet * @author Juergen Hoeller * @since 3.0 * @param the element type */ public class CompositeIterator implements Iterator { private final Set> iterators = new LinkedHashSet<>(); private boolean inUse = false; /** * Add given iterator to this composite. */ public void add(Iterator iterator) { Assert.state(!this.inUse, "You can no longer add iterators to a composite iterator that's already in use"); if (this.iterators.contains(iterator)) { throw new IllegalArgumentException("You cannot add the same iterator twice"); } this.iterators.add(iterator); } @Override public boolean hasNext() { this.inUse = true; for (Iterator iterator : this.iterators) { if (iterator.hasNext()) { return true; } } return false; } @Override public E next() { this.inUse = true; for (Iterator iterator : this.iterators) { if (iterator.hasNext()) { return iterator.next(); } } throw new NoSuchElementException("All iterators exhausted"); } @Override public void remove() { throw new UnsupportedOperationException("CompositeIterator does not support remove()"); } }





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