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 17 package com.google.common.collect; 18 19 import com.google.common.annotations.GwtCompatible; 20 21 import javax.annotation.Nullable; 22 23 /** 24 * Bimap with no mappings. 25 * 26 * @author Jared Levy 27 */ 28 @GwtCompatible(emulated = true) 29 @SuppressWarnings("serial") // uses writeReplace(), not default serialization 30 final class EmptyImmutableBiMap extends ImmutableBiMap<Object, Object> { 31 static final EmptyImmutableBiMap INSTANCE = new EmptyImmutableBiMap(); 32 33 private EmptyImmutableBiMap() {} 34 35 @Override public ImmutableBiMap<Object, Object> inverse() { 36 return this; 37 } 38 39 @Override 40 public int size() { 41 return 0; 42 } 43 44 @Override 45 public boolean isEmpty() { 46 return true; 47 } 48 49 @Override 50 public Object get(@Nullable Object key) { 51 return null; 52 } 53 54 @Override 55 public ImmutableSet<Entry<Object, Object>> entrySet() { 56 return ImmutableSet.of(); 57 } 58 59 @Override 60 ImmutableSet<Entry<Object, Object>> createEntrySet() { 61 throw new AssertionError("should never be called"); 62 } 63 64 @Override 65 public ImmutableSetMultimap<Object, Object> asMultimap() { 66 return ImmutableSetMultimap.of(); 67 } 68 69 @Override 70 public ImmutableSet<Object> keySet() { 71 return ImmutableSet.of(); 72 } 73 74 @Override 75 boolean isPartialView() { 76 return false; 77 } 78 79 Object readResolve() { 80 return INSTANCE; // preserve singleton property 81 } 82 } 83
