Cyclic Iteration : Iterator « Collections « Java Tutorial

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import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.SortedMap;

/** Provide an cyclic {@link Iterator} for a {@link SortedMap}.
 * The {@link Iterator} navigates the entries of the map
 * according to the map's ordering.
 * If the {@link Iterator} hits the last entry of the map,
 * it will then continue from the first entry.
public class CyclicIteration<K, V> implements Iterable<Map.Entry<K, V>> {
  private final SortedMap<K, V> navigablemap;
  private final SortedMap<K, V> tailmap;
  private final K startingkey;

  /** Construct an {@link Iterable} object,
   * so that an {@link Iterator} can be created  
   * for iterating the given {@link SortedMap}.
   * The iteration begins from the starting key exclusively.
  public CyclicIteration(SortedMap<K, V> navigablemap, K startingkey) {
    this.startingkey = startingkey;
    if (navigablemap == null || navigablemap.isEmpty()) {
      this.navigablemap = null;
      this.tailmap = null;
    else {
      this.navigablemap = navigablemap;
      this.tailmap = navigablemap.tailMap(startingkey);

  /** {@inheritDoc} */
  public Iterator<Map.Entry<K, V>> iterator() {
    return new CyclicIterator();

  /** An {@link Iterator} for {@link CyclicIteration}. */
  private class CyclicIterator implements Iterator<Map.Entry<K, V>> {
    private boolean hasnext;
    private Iterator<Map.Entry<K, V>> i;
    /** The first entry to begin. */
    private final Map.Entry<K, V> first;
    /** The next entry. */
    private Map.Entry<K, V> next;
    private CyclicIterator() {
      hasnext = navigablemap != null;
      if (hasnext) {
        i = tailmap.entrySet().iterator();
        Map.Entry<K, V> e = nextEntry();
        if (e.getKey().equals(startingkey)) {
          e = nextEntry();

        first = e; 
        next = first;
      else {
        i = null;
        first = null;
        next = null;

    private Map.Entry<K, V> nextEntry() {
      if (!i.hasNext()) {
        i = navigablemap.entrySet().iterator();

    /** {@inheritDoc} */
    public boolean hasNext() {
      return hasnext;

    /** {@inheritDoc} */
    public Map.Entry<K, V> next() {
      if (!hasnext) {
        throw new NoSuchElementException();

      final Map.Entry<K, V> curr = next;
      next = nextEntry();
      hasnext = !next.equals(first);
      return curr;

    /** Not supported */
    public void remove() {
      throw new UnsupportedOperationException("Not supported");

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.