SupplierWithMemo.java

/*
** Module   : SupplierWithMemo.java
** Abstract : Adds caching functionality to the given supplier.
**
** Copyright (c) 2021, Golden Code Development Corporation.
**
** -#- -I- --Date-- ------------------------------Description----------------------------------
** 001 SBI 20210705 Implemented the supplier that adds caching functionality to the given supplier.
*/
/*
** This program is free software: you can redistribute it and/or modify
** it under the terms of the GNU Affero General Public License as
** published by the Free Software Foundation, either version 3 of the
** License, or (at your option) any later version.
**
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
** GNU Affero General Public License for more details.
**
** You may find a copy of the GNU Affero GPL version 3 at the following
** location: https://www.gnu.org/licenses/agpl-3.0.en.html
** 
** Additional terms under GNU Affero GPL version 3 section 7:
** 
**   Under Section 7 of the GNU Affero GPL version 3, the following additional
**   terms apply to the works covered under the License.  These additional terms
**   are non-permissive additional terms allowed under Section 7 of the GNU
**   Affero GPL version 3 and may not be removed by you.
** 
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** 
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*/

package com.goldencode.p2j.util;

import java.util.concurrent.locks.*;
import java.util.function.*;

/**
 * Adds caching functionality to the given supplier.
 * 
 * @param    <T>
 *           The parametrized type which type value is supplied.
 */
public class SupplierWithMemo<T> implements Supplier<T>
{
   /**
    * The original supplier
    */
   private final Supplier<T> supplier;
   
   /**
    * The cached value
    */
   private T memo;
   
   /**
    * Indicates that memo is set
    */
   private volatile boolean initialized;
   
   /** The read and write synchronizer */
   private ReentrantLock lock = new ReentrantLock();
   
   /**
    * Constructs a supplier with memorization.
    * 
    * @param    supplier
    *           The original supplier.
    */
   public SupplierWithMemo(Supplier<T> supplier)
   {
      this.supplier = supplier;
   }
   
   /**
    * Caches its value and then returns it.
    * 
    * @return   The cached value.
    */
   @Override
   public T get()
   {
      lock.lock();
      try
      {
         if (!initialized)
         {
            memo = supplier.get();
            initialized = true;
         }
         
         return memo;
      }
      finally
      {
         lock.unlock();
      }
   }
}