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.GwtIncompatible; 020import com.google.common.annotations.J2ktIncompatible; 021import com.google.errorprone.annotations.DoNotMock; 022 023/** 024 * Provides similar behavior to {@link String#intern} for any immutable type. Common implementations 025 * are available from the {@link Interners} class. 026 * 027 * <p>Note that {@code String.intern()} has some well-known performance limitations, and should 028 * generally be avoided. Prefer {@link Interners#newWeakInterner} or another {@code Interner} 029 * implementation even for {@code String} interning. 030 * 031 * @author Kevin Bourrillion 032 * @since 3.0 033 */ 034@DoNotMock("Use Interners.new*Interner") 035@J2ktIncompatible 036@GwtIncompatible 037@ElementTypesAreNonnullByDefault 038public interface Interner<E> { 039 /** 040 * Chooses and returns the representative instance for any of a collection of instances that are 041 * equal to each other. If two {@linkplain Object#equals equal} inputs are given to this method, 042 * both calls will return the same instance. That is, {@code intern(a).equals(a)} always holds, 043 * and {@code intern(a) == intern(b)} if and only if {@code a.equals(b)}. Note that {@code 044 * intern(a)} is permitted to return one instance now and a different instance later if the 045 * original interned instance was garbage-collected. 046 * 047 * <p><b>Warning:</b> do not use with mutable objects. 048 * 049 * @throws NullPointerException if {@code sample} is null 050 */ 051 E intern(E sample); 052}