001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017
018package org.apache.commons.lang3.function;
019
020import java.util.function.Supplier;
021
022/**
023 * A functional interface like {@link Supplier} that declares a {@link Throwable}.
024 *
025 * @param <T> Return type.
026 * @param <E> The kind of thrown exception or error.
027 * @since 3.11
028 */
029@FunctionalInterface
030public interface FailableSupplier<T, E extends Throwable> {
031
032    /**
033     * Returns the singleton supplier that always returns null.
034     * <p>
035     * This supplier never throws an exception.
036     * </p>
037     *
038     * @since 3.14.0
039     */
040    @SuppressWarnings("rawtypes")
041    FailableSupplier NUL = () -> null;
042
043    /**
044     * Returns the singleton supplier that always returns null.
045     * <p>
046     * This supplier never throws an exception.
047     * </p>
048     *
049     * @param <T> Supplied type.
050     * @param <E> The kind of thrown exception or error.
051     * @return The NUL singleton.
052     * @since 3.14.0
053     */
054    @SuppressWarnings("unchecked")
055    static <T, E extends Exception> FailableSupplier<T, E> nul() {
056        return NUL;
057    }
058
059    /**
060     * Supplies an object
061     *
062     * @return a result
063     * @throws E if the supplier fails
064     */
065    T get() throws E;
066}