/*
 * 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 org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Legacy version of {@link java.util.function.Supplier java.util.function.Supplier}. Semantically,
 * this could be a factory, generator, builder, closure, or something else entirely. No guarantees
 * are implied by this interface.
 *
 * <p>The {@link Suppliers} class provides common suppliers and related utilities.
 *
 * <p>As this interface extends {@code java.util.function.Supplier}, an instance of this type can be
 * used as a {@code java.util.function.Supplier} directly. To use a {@code
 * java.util.function.Supplier} in a context where a {@code com.google.common.base.Supplier} is
 * needed, use {@code supplier::get}.
 *
 * <p>See the Guava User Guide article on <a
 * href="https://github.com/google/guava/wiki/FunctionalExplained">the use of {@code Function}</a>.
 *
 * @author Harry Heymann
 * @since 2.0
 */
@GwtCompatible
@FunctionalInterface
@ElementTypesAreNonnullByDefault
public interface Supplier<T extends @Nullable Object> extends java.util.function.Supplier<T> {
  /**
   * Retrieves an instance of the appropriate type. The returned object may or may not be a new
   * instance, depending on the implementation.
   *
   * @return an instance of the appropriate type
   */
  @Override
  @ParametricNullness
  T get();
}
