Source code

001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *   http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.reef.util;
020
021import java.util.Collections;
022import java.util.HashSet;
023import java.util.Set;
024
025/**
026 * A helper class that can be used to ensure that objects are only instantiated once.
027 */
028public final class SingletonAsserter {
029
030  private static final Set<Class> CLASSES = Collections.synchronizedSet(new HashSet<Class>());
031
032  /**
033   * This class operates purely in static mode.
034   */
035  private SingletonAsserter() {
036  }
037
038  public static boolean assertSingleton(final Class clazz) {
039    return CLASSES.add(clazz);
040  }
041}