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/*
* Copyright (C) 2008 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.common.collect;
import com.google.common.annotations.GwtCompatible;
import java.util.Map;
import javax.annotation.Nullable;
/**
* An empty immutable map.
*
* @author Jesse Wilson
* @author Kevin Bourrillion
*/
@GwtCompatible(serializable = true, emulated = true)
final class EmptyImmutableMap extends ImmutableMap<Object, Object> {
static final EmptyImmutableMap INSTANCE = new EmptyImmutableMap();
private EmptyImmutableMap() {}
@Override public Object get(@Nullable Object key) {
return null;
}
@Override
public int size() {
return 0;
}
@Override public boolean isEmpty() {
return true;
}
@Override public boolean containsKey(@Nullable Object key) {
return false;
}
@Override public boolean containsValue(@Nullable Object value) {
return false;
}
@Override ImmutableSet<Entry<Object, Object>> createEntrySet() {
throw new AssertionError("should never be called");
}
@Override public ImmutableSet<Entry<Object, Object>> entrySet() {
return ImmutableSet.of();
}
@Override public ImmutableSet<Object> keySet() {
return ImmutableSet.of();
}
@Override public ImmutableCollection<Object> values() {
return ImmutableCollection.EMPTY_IMMUTABLE_COLLECTION;
}
@Override public boolean equals(@Nullable Object object) {
if (object instanceof Map) {
Map<?, ?> that = (Map<?, ?>) object;
return that.isEmpty();
}
return false;
}
@Override boolean isPartialView() {
return false;
}
@Override public int hashCode() {
return 0;
}
@Override public String toString() {
return "{}";
}
Object readResolve() {
return INSTANCE; // preserve singleton property
}
private static final long serialVersionUID = 0;
}
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