Added comments.

Author: iluwatar

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

@@ -1,5 +1,23 @@
 package com.iluwatar;
 
+/**
+ * 
+ * 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. 
+ * 
+ * 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.
+ * 
+ * In this example we have created OliphauntPool inheriting from generic ObjectPool. Oliphaunts 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 {
 
     public static void main( String[] args ) {

object-pool/src/main/java/com/iluwatar/ObjectPool.java

@@ -2,10 +2,16 @@
 
 import java.util.HashSet;
 
+/**
+ * 
+ * Generic object pool
+ *
+ * @param <T>
+ */
 public abstract class ObjectPool<T> {
 
-	HashSet<T> available = new HashSet<>();
-	HashSet<T> inUse = new HashSet<>();
+	private HashSet<T> available = new HashSet<>();
+	private HashSet<T> inUse = new HashSet<>();
 
 	protected abstract T create();
 

object-pool/src/main/java/com/iluwatar/Oliphaunt.java

@@ -1,5 +1,10 @@
 package com.iluwatar;
 
+/**
+ * 
+ * Oliphaunts are expensive to create
+ *
+ */
 public class Oliphaunt {
 
 	private static int counter = 1;
@@ -8,6 +13,11 @@ public class Oliphaunt {
 
 	public Oliphaunt() {
 		id = counter++;
+		try {
+			Thread.sleep(1000);
+		} catch (InterruptedException e) {
+			e.printStackTrace();
+		}
 	}
 
 	public int getId() {

object-pool/src/main/java/com/iluwatar/OliphauntPool.java

@@ -1,5 +1,10 @@
 package com.iluwatar;
 
+/**
+ * 
+ * Oliphaunt object pool
+ *
+ */
 public class OliphauntPool extends ObjectPool<Oliphaunt> {
 
 	@Override