Absent.java
/*
* Copyright 2019 The Android Open Source Project
*
* 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 androidx.camera.core.impl.utils;
import androidx.annotation.Nullable;
import androidx.core.util.Preconditions;
import androidx.core.util.Supplier;
/**
* Implementation of an {@link Optional} not containing a reference.
*
* <p>Copied and adapted from Guava.
*/
final class Absent<T> extends Optional<T> {
static final Absent<Object> sInstance = new Absent<>();
@SuppressWarnings("unchecked") // implementation is "fully variant"
static <T> Optional<T> withType() {
return (Optional<T>) sInstance;
}
private Absent() {
}
@Override
public boolean isPresent() {
return false;
}
@Override
public T get() {
throw new IllegalStateException("Optional.get() cannot be called on an absent value");
}
@Override
public T or(T defaultValue) {
return Preconditions.checkNotNull(defaultValue,
"use Optional.orNull() instead of Optional.or(null)");
}
@SuppressWarnings("unchecked") // safe covariant cast
@Override
public Optional<T> or(Optional<? extends T> secondChoice) {
return (Optional<T>) Preconditions.checkNotNull(secondChoice);
}
@Override
public T or(Supplier<? extends T> supplier) {
return Preconditions.checkNotNull(
supplier.get(), "use Optional.orNull() instead of a Supplier that returns null");
}
@Override
@Nullable
public T orNull() {
return null;
}
@Override
public boolean equals(@Nullable Object object) {
return object == this;
}
@Override
public int hashCode() {
return 0x79a31aac;
}
@Override
public String toString() {
return "Optional.absent()";
}
private Object readResolve() {
return sInstance;
}
private static final long serialVersionUID = 0;
}