001/* 002 * Copyright (C) 2007 The Guava Authors 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * http://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package com.google.common.collect; 018 019import com.google.common.annotations.Beta; 020import com.google.common.annotations.GwtIncompatible; 021import com.google.errorprone.annotations.CanIgnoreReturnValue; 022 023/** 024 * Provides equivalent behavior to {@link String#intern} for other immutable types. Common 025 * implementations are available from the {@link Interners} class. 026 * 027 * @author Kevin Bourrillion 028 * @since 3.0 029 */ 030@Beta 031@GwtIncompatible 032public interface Interner<E> { 033 /** 034 * Chooses and returns the representative instance for any of a collection of instances that are 035 * equal to each other. If two {@linkplain Object#equals equal} inputs are given to this method, 036 * both calls will return the same instance. That is, {@code intern(a).equals(a)} always holds, 037 * and {@code intern(a) == intern(b)} if and only if {@code a.equals(b)}. Note that {@code 038 * intern(a)} is permitted to return one instance now and a different instance later if the 039 * original interned instance was garbage-collected. 040 * 041 * <p><b>Warning:</b> do not use with mutable objects. 042 * 043 * @throws NullPointerException if {@code sample} is null 044 */ 045 @CanIgnoreReturnValue // TODO(cpovirk): Consider removing this? 046 E intern(E sample); 047}