1 /*
2  * Copyright (C) 2007 The Guava Authors
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package com.google.common.collect;
18 
19 import com.google.common.annotations.GwtCompatible;
20 
21 import java.util.Collection;
22 import java.util.Set;
23 
24 import javax.annotation.Nullable;
25 
26 /**
27  * An empty immutable set.
28  *
29  * @author Kevin Bourrillion
30  */
31 @GwtCompatible(serializable = true, emulated = true)
32 final class EmptyImmutableSet extends ImmutableSet<Object> {
33   static final EmptyImmutableSet INSTANCE = new EmptyImmutableSet();
34 
EmptyImmutableSet()35   private EmptyImmutableSet() {}
36 
37   @Override
size()38   public int size() {
39     return 0;
40   }
41 
isEmpty()42   @Override public boolean isEmpty() {
43     return true;
44   }
45 
contains(@ullable Object target)46   @Override public boolean contains(@Nullable Object target) {
47     return false;
48   }
49 
containsAll(Collection<?> targets)50   @Override public boolean containsAll(Collection<?> targets) {
51     return targets.isEmpty();
52   }
53 
iterator()54   @Override public UnmodifiableIterator<Object> iterator() {
55     return Iterators.emptyIterator();
56   }
57 
isPartialView()58   @Override boolean isPartialView() {
59     return false;
60   }
61 
62   @Override
copyIntoArray(Object[] dst, int offset)63   int copyIntoArray(Object[] dst, int offset) {
64     return offset;
65   }
66 
67   @Override
asList()68   public ImmutableList<Object> asList() {
69     return ImmutableList.of();
70   }
71 
equals(@ullable Object object)72   @Override public boolean equals(@Nullable Object object) {
73     if (object instanceof Set) {
74       Set<?> that = (Set<?>) object;
75       return that.isEmpty();
76     }
77     return false;
78   }
79 
hashCode()80   @Override public final int hashCode() {
81     return 0;
82   }
83 
isHashCodeFast()84   @Override boolean isHashCodeFast() {
85     return true;
86   }
87 
toString()88   @Override public String toString() {
89     return "[]";
90   }
91 
readResolve()92   Object readResolve() {
93     return INSTANCE; // preserve singleton property
94   }
95 
96   private static final long serialVersionUID = 0;
97 }
98