Simple object pool : Auto Grow Array « Collections « Java Tutorial

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 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You 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.
 */



/**
 * Simple object pool. Based on ThreadPool and few other classes
 * 
 * The pool will ignore overflow and return null if empty.
 * 
 * @author Gal Shachor
 * @author Costin Manolache
 */
public final class SimplePool {
  /*
   * Where the threads are held.
   */
  private Object pool[];

  private int max;

  private int last;

  private int current = -1;

  private Object lock;

  public static final int DEFAULT_SIZE = 32;

  static final int debug = 0;

  public SimplePool() {
    this(DEFAULT_SIZE, DEFAULT_SIZE);
  }

  public SimplePool(int size) {
    this(size, size);
  }

  public SimplePool(int size, int max) {
    this.max = max;
    pool = new Object[size];
    this.last = size - 1;
    lock = new Object();
  }

  public void set(Object o) {
    put(o);
  }

  /**
   * Add the object to the pool, silent nothing if the pool is full
   */
  public void put(Object o) {
    synchronized (lock) {
      if (current < last) {
        current++;
        pool[current] = o;
      } else if (current < max) {
        // realocate
        int newSize = pool.length * 2;
        if (newSize > max)
          newSize = max + 1;
        Object tmp[] = new Object[newSize];
        last = newSize - 1;
        System.arraycopy(pool, 0, tmp, 0, pool.length);
        pool = tmp;
        current++;
        pool[current] = o;
      }
    }
  }

  /**
   * Get an object from the pool, null if the pool is empty.
   */
  public Object get() {
    Object item = null;
    synchronized (lock) {
      if (current >= 0) {
        item = pool[current];
        pool[current] = null;
        current -= 1;
      }
    }
    return item;
  }

  /**
   * Return the size of the pool
   */
  public int getMax() {
    return max;
  }

  /**
   * Number of object in the pool
   */
  public int getCount() {
    return current + 1;
  }

  public void shutdown() {
  }

}