1 /* 2 * Copyright (C) 2007 The Guava Authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.google.common.collect; 18 19 import com.google.common.annotations.GwtIncompatible; 20 import com.google.common.annotations.J2ktIncompatible; 21 import com.google.errorprone.annotations.DoNotMock; 22 23 /** 24 * Provides similar behavior to {@link String#intern} for any immutable type. Common implementations 25 * are available from the {@link Interners} class. 26 * 27 * <p>Note that {@code String.intern()} has some well-known performance limitations, and should 28 * generally be avoided. Prefer {@link Interners#newWeakInterner} or another {@code Interner} 29 * implementation even for {@code String} interning. 30 * 31 * @author Kevin Bourrillion 32 * @since 3.0 33 */ 34 @DoNotMock("Use Interners.new*Interner") 35 @J2ktIncompatible 36 @GwtIncompatible 37 @ElementTypesAreNonnullByDefault 38 public interface Interner<E> { 39 /** 40 * Chooses and returns the representative instance for any of a collection of instances that are 41 * equal to each other. If two {@linkplain Object#equals equal} inputs are given to this method, 42 * both calls will return the same instance. That is, {@code intern(a).equals(a)} always holds, 43 * and {@code intern(a) == intern(b)} if and only if {@code a.equals(b)}. Note that {@code 44 * intern(a)} is permitted to return one instance now and a different instance later if the 45 * original interned instance was garbage-collected. 46 * 47 * <p><b>Warning:</b> do not use with mutable objects. 48 * 49 * @throws NullPointerException if {@code sample} is null 50 */ intern(E sample)51 E intern(E sample); 52 } 53