org.compass.core.util.IdentityHashSet Maven / Gradle / Ivy
/*
* Copyright 2004-2009 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.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* 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.
*/
package org.compass.core.util;
import java.util.AbstractSet;
import java.util.IdentityHashMap;
import java.util.Iterator;
/**
* @author kimchy
*/
public class IdentityHashSet extends AbstractSet {
private transient IdentityHashMap map;
// Dummy value to associate with an Object in the backing Map
private static final Object PRESENT = new Object();
/**
* Constructs a new, empty set; the backing HashMap instance has
* default initial capacity (16) and load factor (0.75).
*/
public IdentityHashSet() {
map = new IdentityHashMap();
}
/**
* Returns an iterator over the elements in this set. The elements
* are returned in no particular order.
*
* @return an Iterator over the elements in this set.
* @see java.util.ConcurrentModificationException
*/
public Iterator iterator() {
return map.keySet().iterator();
}
/**
* Returns the number of elements in this set (its cardinality).
*
* @return the number of elements in this set (its cardinality).
*/
public int size() {
return map.size();
}
/**
* Returns true if this set contains no elements.
*
* @return true if this set contains no elements.
*/
public boolean isEmpty() {
return map.isEmpty();
}
/**
* Returns true if this set contains the specified element.
*
* @param o element whose presence in this set is to be tested.
* @return true if this set contains the specified element.
*/
public boolean contains(Object o) {
return map.containsKey(o);
}
/**
* Adds the specified element to this set if it is not already
* present.
*
* @param o element to be added to this set.
* @return true if the set did not already contain the specified
* element.
*/
public boolean add(E o) {
return map.put(o, PRESENT) == null;
}
/**
* Removes the specified element from this set if it is present.
*
* @param o object to be removed from this set, if present.
* @return true if the set contained the specified element.
*/
public boolean remove(Object o) {
return map.remove(o) == PRESENT;
}
/**
* Removes all of the elements from this set.
*/
public void clear() {
map.clear();
}
/**
* Returns a shallow copy of this HashSet instance: the elements
* themselves are not cloned.
*
* @return a shallow copy of this set.
*/
public Object clone() {
try {
IdentityHashSet newSet = (IdentityHashSet) super.clone();
newSet.map = (IdentityHashMap) map.clone();
return newSet;
} catch (CloneNotSupportedException e) {
throw new InternalError();
}
}
}