62 lines
2.0 KiB
Java
62 lines
2.0 KiB
Java
/*
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* Copyright (C) 2014 The Dagger Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package dagger.internal;
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import static dagger.internal.Preconditions.checkNotNull;
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import dagger.Lazy;
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/**
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* A {@link Factory} implementation that returns a single instance for all invocations of {@link
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* #get}.
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*
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* <p>Note that while this is a {@link Factory} implementation, and thus unscoped, each call to
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* {@link #get} will always return the same instance. As such, any scoping applied to this factory
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* is redundant and unnecessary. However, using this with {@link DoubleCheck#provider} is valid and
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* may be desired for testing or contractual guarantees.
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*/
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public final class InstanceFactory<T> implements Factory<T>, Lazy<T> {
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public static <T> Factory<T> create(T instance) {
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return new InstanceFactory<T>(checkNotNull(instance, "instance cannot be null"));
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}
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public static <T> Factory<T> createNullable(T instance) {
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return instance == null
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? InstanceFactory.<T>nullInstanceFactory()
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: new InstanceFactory<T>(instance);
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}
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@SuppressWarnings("unchecked") // bivariant implementation
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private static <T> InstanceFactory<T> nullInstanceFactory() {
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return (InstanceFactory<T>) NULL_INSTANCE_FACTORY;
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}
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private static final InstanceFactory<Object> NULL_INSTANCE_FACTORY =
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new InstanceFactory<Object>(null);
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private final T instance;
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private InstanceFactory(T instance) {
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this.instance = instance;
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}
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@Override
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public T get() {
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return instance;
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}
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}
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