1/*
2 * Copyright (C) 2007 Google Inc.
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.android.mail.common.base;
18
19
20/**
21 * A transformation from one object to another. For example, a
22 * {@code StringToIntegerFunction} may implement
23 * <code>Function&lt;String,Integer&gt;</code> and transform integers in
24 * {@code String} format to {@code Integer} format.
25 *
26 * <p>The transformation on the source object does not necessarily result in
27 * an object of a different type.  For example, a
28 * {@code FarenheitToCelsiusFunction} may implement
29 * <code>Function&lt;Float,Float&gt;</code>.
30 *
31 * <p>Implementations which may cause side effects upon evaluation are strongly
32 * encouraged to state this fact clearly in their API documentation.
33 *
34 * @param <F> the type of the function input
35 * @param <T> the type of the function output
36 * @author Kevin Bourrillion
37 * @author Scott Bonneau
38 * @since 2010.01.04 <b>stable</b> (imported from Google Collections Library)
39 */
40public interface Function<F, T> {
41
42  /**
43   * Applies the function to an object of type {@code F}, resulting in an object
44   * of type {@code T}.  Note that types {@code F} and {@code T} may or may not
45   * be the same.
46   *
47   * @param from the source object
48   * @return the resulting object
49   */
50  T apply(F from);
51
52  /**
53   * Indicates whether some other object is equal to this {@code Function}.
54   * This method can return {@code true} <i>only</i> if the specified object is
55   * also a {@code Function} and, for every input object {@code o}, it returns
56   * exactly the same value.  Thus, {@code function1.equals(function2)} implies
57   * that either {@code function1.apply(o)} and {@code function2.apply(o)} are
58   * both null, or {@code function1.apply(o).equals(function2.apply(o))}.
59   *
60   * <p>Note that it is always safe <em>not</em> to override
61   * {@link Object#equals}.
62   */
63  boolean equals(Object obj);
64}
65