Implement LinkedHashSet

This implementation is intentionally simple. If and when the need arises,
we can always implement a more performant version.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

classpath/java/util/LinkedHashSet.java

@@ -0,0 +1,89 @@
+/* Copyright (c) 2008-2013, Avian Contributors
+
+   Permission to use, copy, modify, and/or distribute this software
+   for any purpose with or without fee is hereby granted, provided
+   that the above copyright notice and this permission notice appear
+   in all copies.
+
+   There is NO WARRANTY for this software.  See license.txt for
+   details. */
+
+package java.util;
+
+public class LinkedHashSet<T> extends AbstractSet<T> implements Set<T> {
+  private static final Object Value = new Object();
+
+  private final LinkedHashMap<T, Object> map;
+
+  public LinkedHashSet(Collection<? extends T> c) {
+    map = new LinkedHashMap(c.size());
+    addAll(c);
+  }
+
+  public LinkedHashSet(int capacity) {
+    map = new LinkedHashMap(capacity);
+  }
+
+  public LinkedHashSet() {
+    this(0);
+  }
+
+  public int size() {
+    return map.size();
+  }
+
+  public boolean isEmpty() {
+    return map.isEmpty();
+  }
+
+  public boolean contains(Object element) {
+    return map.containsKey(element);
+  }
+
+  public boolean add(T element) {
+    return map.put(element, Value) != Value;
+  }
+
+  public boolean addAll(Collection<? extends T> collection) {
+    boolean change = false;
+    for (T t: collection) if (add(t)) change = true;
+    return change;
+  }
+
+  public boolean remove(Object element) {
+    return map.remove(element) != Value;
+  }
+
+  public void clear() {
+    map.clear();
+  }
+
+  public Iterator<T> iterator() {
+    return new MyIterator(map.iterator());
+  }
+
+  public String toString() {
+    return Collections.toString(this);
+  }
+
+  private static class MyIterator<T> implements Iterator<T> {
+    private final Iterator<Map.Entry<T, Object>> it;
+
+    public MyIterator(Iterator<Map.Entry<T, Object>> it) {
+      this.it = it;
+    }
+
+    public T next() {
+      return it.next().getKey();
+    }
+
+    public boolean hasNext() {
+      return it.hasNext();
+    }
+
+    public void remove() {
+      it.remove();
+    }
+  }
+}
+