An Iterator that wraps a number of Iterators : Iterator « Collections « Java Tutorial

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import java.util.Iterator;
import java.util.List;

 * An JoinedIterator is an Iterator that wraps a number of Iterators.
 * This class makes multiple iterators look like one to the caller.
 * When any method from the Iterator interface is called, the JoinedIterator
 * will delegate to a single underlying Iterator. The JoinedIterator will
 * invoke the Iterators in sequence until all Iterators are exhausted.
public class JoinedIterator implements Iterator {

  private static final Iterator[] ITERATORS = {};

  // wrapped iterators
  private Iterator[] iterators;

  // index of current iterator in the wrapped iterators array
  private int currentIteratorIndex;

  // the current iterator
  private Iterator currentIterator;

  // the last used iterator
  private Iterator lastUsedIterator;

  public JoinedIterator(List iterators) {
    this( (Iterator[]) iterators.toArray(ITERATORS) );

  public JoinedIterator(Iterator[] iterators) {
    if( iterators==null )
      throw new NullPointerException("Unexpected NULL iterators argument");
    this.iterators = iterators;

  public JoinedIterator(Iterator first, Iterator second) {
    this( new Iterator[] { first, second } );

  public boolean hasNext() {
    return currentIterator.hasNext();

  public Object next() {

  public void remove() {

  // call this before any Iterator method to make sure that the current Iterator
  // is not exhausted
  protected void updateCurrentIterator() {

    if (currentIterator == null) {
      if( iterators.length==0  ) {
        currentIterator = EmptyIterator.emptyIterator;
      else {
        currentIterator = iterators[0];
      // set last used iterator here, in case the user calls remove
      // before calling hasNext() or next() (although they shouldn't)
      lastUsedIterator = currentIterator;

    while (! currentIterator.hasNext() && currentIteratorIndex < iterators.length - 1) {
      currentIterator = iterators[currentIteratorIndex];

/*   Copyright 2004 BEA Systems, Inc.
*   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
*   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.

class EmptyIterator implements java.util.Iterator {
 public static final EmptyIterator emptyIterator = new EmptyIterator();
 public boolean hasNext() { return false; }
 public Object next() { return null; }
 public void remove() {
   throw new UnsupportedOperationException();

9.37.1.Use Iterator to loop through ArrayList
9.37.2.Use Iterator to loop through the HashMap class
9.37.3.Iterate through a Collection using Java Iterator
9.37.4.Traverse through ArrayList in forward direction using Java ListIterator
9.37.5.Traverse through ArrayList in reverse direction using Java ListIterator
9.37.6.Iterate a Collection and remove an item (Exception, wrong version)
9.37.7.Remove an element from Collection using Java Iterator
9.37.8.Iterator from LinkedList
9.37.9.Iterate through elements of Java LinkedList using Iterator
9.37.10.An Iterator that wraps a number of Iterators
9.37.11.Array Iterator
9.37.12.Create singleton Iterator
9.37.13.Cyclic Iteration
9.37.14.Iterator Union of Iterators
9.37.15.Iterator Utils
9.37.16.Iterator class for sparse values in an array.
9.37.17.Iterator class for values contained in an array range.
9.37.18.Sorted Iterator
9.37.19.Treat an Iterator as an Iterable
9.37.20.An Iterator that returns the elements of a specified array, or other iterators etc.
9.37.21.An Iterator wrapper for an Enumeration.
9.37.22.An Iterator wrapper for an Object[], allow us to deal with all array like structures in a consistent manner.
9.37.23.An iterator that breaks text into lines. The result is equal to BufferedReader.readLine().
9.37.24.Gets the child of the specified element having the specified unique name
9.37.25.Implements an java.util.Iterator over any array
9.37.26.Protects an given iterator by preventing calls to remove().
9.37.27.Returns an iterator over the children of the given element with the given tag name
9.37.28.Use an Iterator to cycle through a collection in the forward direction.
9.37.29.This constructs an Iterator over each day in a date range defined by a focus date and range style.