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/*
* Copyright (C) 2011 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.base;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.annotations.GwtCompatible;
import java.util.Collections;
import java.util.Set;
import javax.annotation.Nullable;
/**
* Implementation of an {@link Optional} not containing a reference.
*/
@GwtCompatible
final class Absent extends Optional<Object> {
static final Absent INSTANCE = new Absent();
private Absent() {}
@Override public boolean isPresent() {
return false;
}
@Override public Object get() {
throw new IllegalStateException("Optional.get() cannot be called on an absent value");
}
@Override public Object or(Object defaultValue) {
return checkNotNull(defaultValue, "use Optional.orNull() instead of Optional.or(null)");
}
@SuppressWarnings("unchecked") // safe covariant cast
@Override public Optional<Object> or(Optional<?> secondChoice) {
return (Optional) checkNotNull(secondChoice);
}
@Override public Object or(Supplier<?> supplier) {
return checkNotNull(supplier.get(),
"use Optional.orNull() instead of a Supplier that returns null");
}
@Override @Nullable public Object orNull() {
return null;
}
@Override public Set<Object> asSet() {
return Collections.emptySet();
}
@Override public <V> Optional<V> transform(Function<Object, V> function) {
checkNotNull(function);
return Optional.absent();
}
@Override public boolean equals(@Nullable Object object) {
return object == this;
}
@Override public int hashCode() {
return 0x598df91c;
}
@Override public String toString() {
return "Optional.absent()";
}
private Object readResolve() {
return INSTANCE;
}
private static final long serialVersionUID = 0;
}
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