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/*
 * Copyright 2023 dorkbox, llc
 *
 * 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 dorkbox.collections;

import java.util.AbstractSet;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.Set;

public
class IdentitySet extends AbstractSet implements Set, Cloneable, java.io.Serializable {
    private transient IdentityMap 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
    IdentitySet() {
        map = new IdentityMap<>();
    }

    /**
     * Constructs a new set containing the elements in the specified
     * collection.  The HashMap is created with default load factor
     * (0.75) and an initial capacity sufficient to contain the elements in
     * the specified collection.
     *
     * @param c the collection whose elements are to be placed into this set
     *
     * @throws NullPointerException if the specified collection is null
     */
    public
    IdentitySet(Collection c) {
        map = new IdentityMap<>(Math.max((int) (c.size() / .75f) + 1, 16));
        addAll(c);
    }

    /**
     * Constructs a new, empty set; the backing HashMap instance has
     * the specified initial capacity and default load factor (0.75).
     *
     * @param initialCapacity the initial capacity of the hash table
     *
     * @throws IllegalArgumentException if the initial capacity is less
     *         than zero
     */
    public
    IdentitySet(int initialCapacity) {
        map = new IdentityMap<>(initialCapacity);
    }

    /**
     * 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 ConcurrentModificationException
     */
    @Override
    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)
     */
    @Override
    public
    int size() {
        return map.size();
    }

    /**
     * Returns true if this set contains no elements.
     *
     * @return true if this set contains no elements
     */
    @Override
    public
    boolean isEmpty() {
        return map.isEmpty();
    }

    /**
     * Returns true if this set contains the specified element.
     * More formally, returns true if and only if this set
     * contains an element e such that
     * (o==null ? e==null : o.equals(e)).
     *
     * @param o element whose presence in this set is to be tested
     *
     * @return true if this set contains the specified element
     */
    @Override
    public
    boolean contains(Object o) {
        return map.containsKey(o);
    }

    /**
     * Adds the specified element to this set if it is not already present.
     * More formally, adds the specified element e to this set if
     * this set contains no element e2 such that
     * (e==null ? e2==null : e.equals(e2)).
     * If this set already contains the element, the call leaves the set
     * unchanged and returns false.
     *
     * @param e element to be added to this set
     *
     * @return true if this set did not already contain the specified
     *         element
     */
    @Override
    public
    boolean add(E e) {
        return map.put(e, PRESENT) == null;
    }

    /**
     * Removes the specified element from this set if it is present.
     * More formally, removes an element e such that
     * (o==null ? e==null : o.equals(e)),
     * if this set contains such an element.  Returns true if
     * this set contained the element (or equivalently, if this set
     * changed as a result of the call).  (This set will not contain the
     * element once the call returns.)
     *
     * @param o object to be removed from this set, if present
     *
     * @return true if the set contained the specified element
     */
    @Override
    public
    boolean remove(Object o) {
        return map.remove(o) == PRESENT;
    }

    /**
     * Removes all of the elements from this set.
     * The set will be empty after this call returns.
     */
    @Override
    public
    void clear() {
        map.clear();
    }
}




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