java-design-patterns/object-pool/src/main/java/com/iluwatar/object/pool/App.java

package com.iluwatar.object.pool;

/**
 * 
 * When it is necessary to work with a large number of objects that are particularly expensive to
 * instantiate and each object is only needed for a short period of time, the performance of an
 * entire application may be adversely affected. An object pool design pattern may be deemed
 * desirable in cases such as these.
 * <p>
 * The object pool design pattern creates a set of objects that may be reused. When a new object is
 * needed, it is requested from the pool. If a previously prepared object is available it is
 * returned immediately, avoiding the instantiation cost. If no objects are present in the pool, a
 * new item is created and returned. When the object has been used and is no longer needed, it is
 * returned to the pool, allowing it to be used again in the future without repeating the
 * computationally expensive instantiation process. It is important to note that once an object has
 * been used and returned, existing references will become invalid.
 * <p>
 * In this example we have created {@link OliphauntPool} inheriting from generic {@link ObjectPool}.
 * {@link Oliphaunt}s can be checked out from the pool and later returned to it. The pool tracks
 * created instances and their status (available, inUse).
 *
 */
public class App {

  /**
   * Program entry point
   * 
   * @param args command line args
   */
  public static void main(String[] args) {
    OliphauntPool pool = new OliphauntPool();
    System.out.println(pool);
    Oliphaunt oliphaunt1 = pool.checkOut();
    System.out.println("Checked out " + oliphaunt1);
    System.out.println(pool);
    Oliphaunt oliphaunt2 = pool.checkOut();
    System.out.println("Checked out " + oliphaunt2);
    Oliphaunt oliphaunt3 = pool.checkOut();
    System.out.println("Checked out " + oliphaunt3);
    System.out.println(pool);
    System.out.println("Checking in " + oliphaunt1);
    pool.checkIn(oliphaunt1);
    System.out.println("Checking in " + oliphaunt2);
    pool.checkIn(oliphaunt2);
    System.out.println(pool);
    Oliphaunt oliphaunt4 = pool.checkOut();
    System.out.println("Checked out " + oliphaunt4);
    Oliphaunt oliphaunt5 = pool.checkOut();
    System.out.println("Checked out " + oliphaunt5);
    System.out.println(pool);
  }
}