Examples of java.util.IdentityHashMap.keySet()

java.util.IdentityHashMap.keySet()
Returns an identity-based set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress, the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll, and clear methods. It does not support the add or addAll methods.
While the object returned by this method implements the Set interface, it does not obey Set's general contract. Like its backing map, the set returned by this method defines element equality as reference-equality rather than object-equality. This affects the behavior of its contains, remove, containsAll, equals, and hashCode methods.
The equals method of the returned set returns true only if the specified object is a set containing exactly the same object references as the returned set. The symmetry and transitivity requirements of the Object.equals contract may be violated if the set returned by this method is compared to a normal set. However, the Object.equals contract is guaranteed to hold among sets returned by this method.
The hashCode method of the returned set returns the sum of the identity hashcodes of the elements in the set, rather than the sum of their hashcodes. This is mandated by the change in the semantics of the equals method, in order to enforce the general contract of the Object.hashCode method among sets returned by this method. @return an identity-based set view of the keys contained in this map @see Object#equals(Object) @see System#identityHashCode(Object)

    map.put("key", "value");
    map.put(null, null);
    map.put("a key", null);
    map.put("another key", null);


    Set keyset = map.keySet();
    Collection valueset = map.values();
    Set entries = map.entrySet();
    Iterator it = entries.iterator();
    while (it.hasNext()) {
      Map.Entry entry = (Map.Entry) it.next();

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  public void test_keySet_clear() {
    IdentityHashMap map = new IdentityHashMap();
    for (int i = 0; i < 1000; i++) {
      map.put(new Integer(i), new Integer(i));
    }
    Set set = map.keySet();
    set.clear();


    assertEquals("did not remove all elements in the map", 0, map.size());
    assertTrue("did not remove all elements in the keyset", set.isEmpty());

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  public void test_keySet_removeAll() {
    IdentityHashMap map = new IdentityHashMap();
    for (int i = 0; i < 1000; i++) {
      map.put(new Integer(i), new Integer(i));
    }
    Set set = map.keySet();
    set.removeAll(set);


    assertEquals("did not remove all elements in the map", 0, map.size());
    assertTrue("did not remove all elements in the keyset", set.isEmpty());

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  public void test_keySet_retainAll() {
    IdentityHashMap map = new IdentityHashMap();
    for (int i = 0; i < 1000; i++) {
      map.put(new Integer(i), new Integer(i));
    }
    Set set = map.keySet();


    // retain all the elements
    boolean result = set.retainAll(set);
    assertTrue("retain all should return false", !result);
    assertEquals("did not retain all", 1000, set.size());

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    map.put(new Integer(61), null);
    map.put(new Integer(71), null);
    map.put(new Integer(81), null);
    map.put(new Integer(91), null);


    Set set = map.keySet();


    Set newset = new HashSet();
    Iterator it = set.iterator();
    while (it.hasNext()) {
      Object element = it.next();

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        Map map3 = Collections.EMPTY_MAP;
        assertSame("EMPTY_MAP", map3.keySet(), map3.keySet());


        AbstractMap map4 = new IdentityHashMap(1);
        assertSame("IdentityHashMap", map4.keySet(), map4.keySet());


        AbstractMap map5 = new LinkedHashMap(122);
        assertSame("LinkedHashMap", map5.keySet(), map5.keySet());


        AbstractMap map6 = new TreeMap();

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        Map map3 = Collections.EMPTY_MAP;
        assertSame("EMPTY_MAP", map3.keySet(), map3.keySet());


        AbstractMap map4 = new IdentityHashMap(1);
        assertSame("IdentityHashMap", map4.keySet(), map4.keySet());


        AbstractMap map5 = new LinkedHashMap(122);
        assertSame("LinkedHashMap", map5.keySet(), map5.keySet());


        AbstractMap map6 = new TreeMap();

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          .get(objArray2[counter]) == hm2.get(objArray2[counter]));


    IdentityHashMap map = new IdentityHashMap();
    map.put("key", "value");
    // get the keySet() and values() on the original Map
    Set keys = map.keySet();
    Collection values = map.values();
    assertEquals("values() does not work", 
        "value", values.iterator().next());
    assertEquals("keySet() does not work", 
        "key", keys.iterator().next());

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          .contains(objArray2[i]));
    }


    IdentityHashMap m = new IdentityHashMap();
    m.put(null, "test");
    assertTrue("Failed with null key", m.keySet().contains(null));
    assertNull("Failed with null key", m.keySet().iterator().next());


    Map map = new IdentityHashMap(101);
    map.put(new Integer(1), "1");
    map.put(new Integer(102), "102");

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    }


    IdentityHashMap m = new IdentityHashMap();
    m.put(null, "test");
    assertTrue("Failed with null key", m.keySet().contains(null));
    assertNull("Failed with null key", m.keySet().iterator().next());


    Map map = new IdentityHashMap(101);
    map.put(new Integer(1), "1");
    map.put(new Integer(102), "102");
    map.put(new Integer(203), "203");

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