Polishing

spring-core/src/main/java/org/springframework/util/CompositeIterator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2014 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.
@@ -13,46 +13,48 @@
  * 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.LinkedList;
-import java.util.List;
+import java.util.LinkedHashSet;
 import java.util.NoSuchElementException;
+import java.util.Set;
 
 /**
- * Iterator that combines multiple other iterators.
- * This implementation maintains a list of iterators which are invoked in sequence until all iterators are exhausted.
+ * Composite iterator that combines multiple other iterators,
+ * as registered via {@link #add(Iterator)}.
+ *
+ * <p>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
  */
 public class CompositeIterator<E> implements Iterator<E> {
 
-	private List<Iterator<E>> iterators = new LinkedList<Iterator<E>>();
+	private final Set<Iterator<E>> iterators = new LinkedHashSet<Iterator<E>>();
 
 	private boolean inUse = false;
 
-	/**
-	 * Create a new composite iterator. Add iterators using the {@link #add(Iterator)} method.
-	 */
-	public CompositeIterator() {
-	}
 
 	/**
 	 * Add given iterator to this composite.
 	 */
 	public void add(Iterator<E> iterator) {
-		Assert.state(!inUse, "You can no longer add iterator to a composite iterator that's already in use");
-		if (iterators.contains(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");
 		}
-		iterators.add(iterator);
+		this.iterators.add(iterator);
 	}
 
 	@Override
 	public boolean hasNext() {
-		inUse = true;
-		for (Iterator<Iterator<E>> it = iterators.iterator(); it.hasNext();) {
-			if (it.next().hasNext()) {
+		this.inUse = true;
+		for (Iterator<E> iterator : this.iterators) {
+			if (iterator.hasNext()) {
 				return true;
 			}
 		}
@@ -61,18 +63,18 @@ public class CompositeIterator<E> implements Iterator<E> {
 
 	@Override
 	public E next() {
-		inUse = true;
-		for (Iterator<Iterator<E>> it = iterators.iterator(); it.hasNext();) {
-			Iterator<E> iterator = it.next();
+		this.inUse = true;
+		for (Iterator<E> iterator : this.iterators) {
 			if (iterator.hasNext()) {
 				return iterator.next();
 			}
 		}
-		throw new NoSuchElementException("Exhausted all iterators");
+		throw new NoSuchElementException("All iterators exhausted");
 	}
 
 	@Override
 	public void remove() {
-		throw new UnsupportedOperationException("Remove is not supported");
+		throw new UnsupportedOperationException("CompositeIterator does not support remove()");
 	}
+
 }