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
17package com.google.common.collect;
18
19import com.google.common.annotations.Beta;
20
21/**
22 * Provides equivalent behavior to {@link String#intern} for other immutable
23 * types.
24 *
25 * @author Kevin Bourrillion
26 * @since 3.0
27 */
28@Beta
29public interface Interner<E> {
30  /**
31   * Chooses and returns the representative instance for any of a collection of
32   * instances that are equal to each other. If two {@linkplain Object#equals
33   * equal} inputs are given to this method, both calls will return the same
34   * instance.  That is, {@code intern(a).equals(a)} always holds, and {@code
35   * intern(a) == intern(b)} if and only if {@code a.equals(b)}. Note that
36   * {@code intern(a)} is permitted to return one instance now and a different
37   * instance later if the original interned instance was garbage-collected.
38   *
39   * <p><b>Warning:</b> do not use with mutable objects.
40   *
41   * @throws NullPointerException if {@code sample} is null
42   */
43  E intern(E sample);
44}
45