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