| /* |
| * Copyright (C) 2007 The Guava Authors |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except |
| * in compliance with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software distributed under the License |
| * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express |
| * or implied. See the License for the specific language governing permissions and limitations under |
| * the License. |
| */ |
| |
| package com.google.common.base; |
| |
| import com.google.common.annotations.GwtCompatible; |
| import com.google.errorprone.annotations.CanIgnoreReturnValue; |
| import org.checkerframework.checker.nullness.compatqual.NullableDecl; |
| |
| /** |
| * Determines an output value based on an input value; a pre-Java-8 version of {@link |
| * java.util.function.Function java.util.function.Function}. |
| * |
| * <p>The {@link Functions} class provides common functions and related utilities. |
| * |
| * <p>See the Guava User Guide article on <a |
| * href="https://github.com/google/guava/wiki/FunctionalExplained">the use of {@code Function}</a>. |
| * |
| * <h3>For Java 8+ users</h3> |
| * |
| * <p>This interface is now a legacy type. Use {@code java.util.function.Function} (or the |
| * appropriate primitive specialization such as {@code ToIntFunction}) instead whenever possible. |
| * Otherwise, at least reduce <i>explicit</i> dependencies on this type by using lambda expressions |
| * or method references instead of classes, leaving your code easier to migrate in the future. |
| * |
| * <p>To use an existing function (say, named {@code function}) in a context where the <i>other |
| * type</i> of function is expected, use the method reference {@code function::apply}. A future |
| * version of {@code com.google.common.base.Function} will be made to <i>extend</i> {@code |
| * java.util.function.Function}, making conversion code necessary only in one direction. At that |
| * time, this interface will be officially discouraged. |
| * |
| * @author Kevin Bourrillion |
| * @since 2.0 |
| */ |
| @GwtCompatible |
| public interface Function<F, T> { |
| /** |
| * Returns the result of applying this function to {@code input}. This method is <i>generally |
| * expected</i>, but not absolutely required, to have the following properties: |
| * |
| * <ul> |
| * <li>Its execution does not cause any observable side effects. |
| * <li>The computation is <i>consistent with equals</i>; that is, {@link Objects#equal |
| * Objects.equal}{@code (a, b)} implies that {@code Objects.equal(function.apply(a), |
| * function.apply(b))}. |
| * </ul> |
| * |
| * @throws NullPointerException if {@code input} is null and this function does not accept null |
| * arguments |
| */ |
| @CanIgnoreReturnValue // TODO(kevinb): remove this |
| @NullableDecl |
| T apply(@NullableDecl F input); |
| |
| /** |
| * <i>May</i> return {@code true} if {@code object} is a {@code Function} that behaves identically |
| * to this function. |
| * |
| * <p><b>Warning: do not depend</b> on the behavior of this method. |
| * |
| * <p>Historically, {@code Function} instances in this library have implemented this method to |
| * recognize certain cases where distinct {@code Function} instances would in fact behave |
| * identically. However, as code migrates to {@code java.util.function}, that behavior will |
| * disappear. It is best not to depend on it. |
| */ |
| @Override |
| boolean equals(@NullableDecl Object object); |
| } |