Memoize.java

/*
 * *********************************************************************************************************************
 *
 * blueMarine II: Semantic Media Centre
 * http://tidalwave.it/projects/bluemarine2
 *
 * Copyright (C) 2015 - 2021 by Tidalwave s.a.s. (http://tidalwave.it)
 *
 * *********************************************************************************************************************
 *
 * 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.
 *
 * *********************************************************************************************************************
 *
 * git clone https://bitbucket.org/tidalwave/bluemarine2-src
 * git clone https://github.com/tidalwave-it/bluemarine2-src
 *
 * *********************************************************************************************************************
 */
package it.tidalwave.util;

import javax.annotation.Nonnull;
import java.util.function.Supplier;
import static java.util.Objects.requireNonNull;

/***********************************************************************************************************************
 *
 * @author  Fabrizio Giudici
 *
 **********************************************************************************************************************/
public class Memoize<T>
  {
    private T value;

    private transient volatile boolean initialized;

    private transient volatile Supplier<T> supplier;

    public Memoize()
      {
      }

    public Memoize (@Nonnull final Supplier<T> supplier)
      {
        this.supplier = supplier;
      }

    @Nonnull
    public T get()
      {
        return get(requireNonNull(supplier, "get() can be used if the Supplier has been provided in the constructor"));
      }

    @Nonnull
    public T get (@Nonnull final Supplier<T> supplier)
      {
        if (!initialized) // double checked locking
          {
            synchronized (this)
              {
                if (!initialized)
                  {
                    value = supplier.get();
                    initialized = true;
                  }
              }
          }

        return value;
      }
  }