1/* 2 * Copyright (C) 2008 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 17package com.google.common.collect; 18 19import com.google.common.annotations.GwtCompatible; 20 21import java.util.Map; 22 23import javax.annotation.Nullable; 24 25/** 26 * An empty immutable map. 27 * 28 * @author Jesse Wilson 29 * @author Kevin Bourrillion 30 */ 31@GwtCompatible(serializable = true, emulated = true) 32final class EmptyImmutableMap extends ImmutableMap<Object, Object> { 33 static final EmptyImmutableMap INSTANCE = new EmptyImmutableMap(); 34 35 private EmptyImmutableMap() {} 36 37 @Override public Object get(@Nullable Object key) { 38 return null; 39 } 40 41 @Override 42 public int size() { 43 return 0; 44 } 45 46 @Override public boolean isEmpty() { 47 return true; 48 } 49 50 @Override public boolean containsKey(@Nullable Object key) { 51 return false; 52 } 53 54 @Override public boolean containsValue(@Nullable Object value) { 55 return false; 56 } 57 58 @Override public ImmutableSet<Entry<Object, Object>> entrySet() { 59 return ImmutableSet.of(); 60 } 61 62 @Override public ImmutableSet<Object> keySet() { 63 return ImmutableSet.of(); 64 } 65 66 @Override public ImmutableCollection<Object> values() { 67 return ImmutableCollection.EMPTY_IMMUTABLE_COLLECTION; 68 } 69 70 @Override public boolean equals(@Nullable Object object) { 71 if (object instanceof Map) { 72 Map<?, ?> that = (Map<?, ?>) object; 73 return that.isEmpty(); 74 } 75 return false; 76 } 77 78 @Override boolean isPartialView() { 79 return false; 80 } 81 82 @Override public int hashCode() { 83 return 0; 84 } 85 86 @Override public String toString() { 87 return "{}"; 88 } 89 90 Object readResolve() { 91 return INSTANCE; // preserve singleton property 92 } 93 94 private static final long serialVersionUID = 0; 95} 96