Indexed Set : Set « Collections Data Structure « Java

Indexed Set

//package gr.forth.ics.util;

import java.util.AbstractCollection;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

 * @author  Andreou Dimitris, email: jim.andreou (at) gmail (dot) com 
public class IndexedSet<T> extends AbstractCollection<T> implements Set<T> {
    private final List<T> list = new ArrayList<T>();
    private final Set<T> set = new HashSet<T>();
    public int size() {
        return list.size();

    public boolean isEmpty() {
        return list.isEmpty();

    public boolean contains(Object o) {
        return set.contains(o);

    public Iterator<T> iterator() {
        return new Iterator<T>() {
            Iterator<T> realIterator = list.iterator();
            T current = null;

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

            public T next() {
                T next =;
                current = next;
                return next;

            public void remove() {
                current = null;

    public Object[] toArray() {
        return list.toArray();

    public <T> T[] toArray(T[] a) {
        return list.toArray(a);

    public boolean add(T e) {
        boolean added = set.add(e);
        if (added) {
        return added;

    public boolean remove(Object o) {
        boolean removed = set.remove(o);
        if (removed) {
        return removed;

    public boolean containsAll(Collection<?> c) {
        return set.containsAll(c);

    public boolean retainAll(Collection<?> c) {
        boolean removed = false;
        Iterator<T> it = list.iterator();
        while (it.hasNext()) {
            T next =;
            if (!c.contains(next)) {
                removed = true;
        return removed;

    public void clear() {

    public T get(int index) {
        return list.get(index);

    public T remove(int index) {
        T t = list.get(index);
        return t;


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