001/* 002 * Copyright (C) 2007 The Guava Authors 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except 005 * in compliance with the License. You may obtain a copy of the License at 006 * 007 * http://www.apache.org/licenses/LICENSE-2.0 008 * 009 * Unless required by applicable law or agreed to in writing, software distributed under the License 010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express 011 * or implied. See the License for the specific language governing permissions and limitations under 012 * the License. 013 */ 014 015package com.google.common.base; 016 017import com.google.common.annotations.GwtCompatible; 018import com.google.errorprone.annotations.CanIgnoreReturnValue; 019import org.checkerframework.checker.nullness.qual.Nullable; 020 021/** 022 * A class that can supply objects of a single type; a pre-Java-8 version of {@link 023 * java.util.function.Supplier java.util.function.Supplier}. Semantically, this could be a factory, 024 * generator, builder, closure, or something else entirely. No guarantees are implied by this 025 * interface. 026 * 027 * <p>The {@link Suppliers} class provides common suppliers and related utilities. 028 * 029 * <p>See the Guava User Guide article on <a href= 030 * "https://github.com/google/guava/wiki/FunctionalExplained">the use of functional types</a>. 031 * 032 * <h3>For Java 8+ users</h3> 033 * 034 * <p>This interface is now a legacy type. Use {@code java.util.function.Supplier} (or the 035 * appropriate primitive specialization such as {@code IntSupplier}) instead whenever possible. 036 * Otherwise, at least reduce <i>explicit</i> dependencies on this type by using lambda expressions 037 * or method references instead of classes, leaving your code easier to migrate in the future. 038 * 039 * <p>To use an existing supplier instance (say, named {@code supplier}) in a context where the 040 * <i>other type</i> of supplier is expected, use the method reference {@code supplier::get}. A 041 * future version of {@code com.google.common.base.Supplier} will be made to <i>extend</i> {@code 042 * java.util.function.Supplier}, making conversion code necessary only in one direction. At that 043 * time, this interface will be officially discouraged. 044 * 045 * @author Harry Heymann 046 * @since 2.0 047 */ 048@GwtCompatible 049@ElementTypesAreNonnullByDefault 050public interface Supplier<T extends @Nullable Object> { 051 /** 052 * Retrieves an instance of the appropriate type. The returned object may or may not be a new 053 * instance, depending on the implementation. 054 * 055 * @return an instance of the appropriate type 056 */ 057 @CanIgnoreReturnValue 058 @ParametricNullness 059 T get(); 060}