1/* 2 * Copyright (C) 2009 Google Inc. 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 static com.google.common.base.Preconditions.checkNotNull; 20 21import com.google.common.annotations.GwtCompatible; 22 23import java.util.Map; 24 25import javax.annotation.Nullable; 26import javax.annotation.concurrent.Immutable; 27 28/** 29 * An empty implementation of {@link ImmutableTable}. 30 * 31 * @author gak@google.com (Gregory Kick) 32 */ 33@GwtCompatible 34@Immutable 35final class EmptyImmutableTable extends ImmutableTable<Object, Object, Object> { 36 static final EmptyImmutableTable INSTANCE = new EmptyImmutableTable(); 37 38 private EmptyImmutableTable() {} 39 40 @Override public int size() { 41 return 0; 42 } 43 44 @Override public Object get(@Nullable Object rowKey, 45 @Nullable Object columnKey) { 46 return null; 47 } 48 49 @Override public boolean isEmpty() { 50 return true; 51 } 52 53 @Override public boolean equals(@Nullable Object obj) { 54 if (obj == this) { 55 return true; 56 } else if (obj instanceof Table<?, ?, ?>) { 57 Table<?, ?, ?> that = (Table<?, ?, ?>) obj; 58 return that.isEmpty(); 59 } else { 60 return false; 61 } 62 } 63 64 @Override public int hashCode() { 65 return 0; 66 } 67 68 @Override public ImmutableSet<Cell<Object, Object, Object>> cellSet() { 69 return ImmutableSet.of(); 70 } 71 72 @Override public ImmutableMap<Object, Object> column(Object columnKey) { 73 checkNotNull(columnKey); 74 return ImmutableMap.of(); 75 } 76 77 @Override public ImmutableSet<Object> columnKeySet() { 78 return ImmutableSet.of(); 79 } 80 81 @Override public ImmutableMap<Object, Map<Object, Object>> columnMap() { 82 return ImmutableMap.of(); 83 } 84 85 @Override public boolean contains(@Nullable Object rowKey, 86 @Nullable Object columnKey) { 87 return false; 88 } 89 90 @Override public boolean containsColumn(@Nullable Object columnKey) { 91 return false; 92 } 93 94 @Override public boolean containsRow(@Nullable Object rowKey) { 95 return false; 96 } 97 98 @Override public boolean containsValue(@Nullable Object value) { 99 return false; 100 } 101 102 @Override public ImmutableMap<Object, Object> row(Object rowKey) { 103 checkNotNull(rowKey); 104 return ImmutableMap.of(); 105 } 106 107 @Override public ImmutableSet<Object> rowKeySet() { 108 return ImmutableSet.of(); 109 } 110 111 @Override public ImmutableMap<Object, Map<Object, Object>> rowMap() { 112 return ImmutableMap.of(); 113 } 114 115 @Override public String toString() { 116 return "{}"; 117 } 118 119 @Override public ImmutableCollection<Object> values() { 120 return ImmutableSet.of(); 121 } 122 123 Object readResolve() { 124 return INSTANCE; // preserve singleton property 125 } 126 127 private static final long serialVersionUID = 0; 128} 129