com.google.common.collect.Interner Maven / Gradle / Ivy
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/*
* Copyright (C) 2007 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.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import com.google.errorprone.annotations.DoNotMock;
/**
* Provides similar behavior to {@link String#intern} for any immutable type. Common implementations
* are available from the {@link Interners} class.
*
* Note that {@code String.intern()} has some well-known performance limitations, and should
* generally be avoided. Prefer {@link Interners#newWeakInterner} or another {@code Interner}
* implementation even for {@code String} interning.
*
* @author Kevin Bourrillion
* @since 3.0
*/
@DoNotMock("Use Interners.new*Interner")
@J2ktIncompatible
@GwtIncompatible
@ElementTypesAreNonnullByDefault
public interface Interner {
/**
* Chooses and returns the representative instance for any of a collection of instances that are
* equal to each other. If two {@linkplain Object#equals equal} inputs are given to this method,
* both calls will return the same instance. That is, {@code intern(a).equals(a)} always holds,
* and {@code intern(a) == intern(b)} if and only if {@code a.equals(b)}. Note that {@code
* intern(a)} is permitted to return one instance now and a different instance later if the
* original interned instance was garbage-collected.
*
* Warning: do not use with mutable objects.
*
* @throws NullPointerException if {@code sample} is null
*/
E intern(E sample);
}