Commented the example.

private-class-data/src/main/java/com/iluwatar/App.java

@@ -1,13 +1,33 @@
 package com.iluwatar;
 
+/**
+ * 
+ * The Private Class Data design pattern seeks to reduce exposure of attributes 
+ * by limiting their visibility. It reduces the number of class attributes by 
+ * encapsulating them in single data object. It allows the class designer to 
+ * remove write privilege of attributes that are intended to be set only during 
+ * construction, even from methods of the target class.
+ * 
+ * In the example we have normal Stew class with some ingredients given in
+ * constructor. Then we have methods to enumerate the ingredients and to taste
+ * the stew. The method for tasting the stew alters the private members of the
+ * stew class.
+ * 
+ * The problem is solved with the Private Class Data pattern. We introduce
+ * ImmutableStew class that contains StewData. The private data members of
+ * Stew are now in StewData and cannot be altered by ImmutableStew methods.
+ *
+ */
 public class App {
 	
     public static void main( String[] args ) {
+    	// stew is mutable
     	Stew stew = new Stew(1, 2, 3, 4);
     	stew.mix();
     	stew.taste();
     	stew.mix();
     	
+    	// immutable stew protected with Private Class Data pattern
     	ImmutableStew immutableStew = new ImmutableStew(2, 4, 3, 6);
     	immutableStew.mix();
     }

private-class-data/src/main/java/com/iluwatar/ImmutableStew.java

@@ -1,5 +1,10 @@
 package com.iluwatar;
 
+/**
+ * 
+ * Immutable stew class, protected with Private Class Data pattern
+ *
+ */
 public class ImmutableStew {
 
 	private StewData data;

private-class-data/src/main/java/com/iluwatar/Stew.java

@@ -1,5 +1,10 @@
 package com.iluwatar;
 
+/**
+ * 
+ * Mutable stew class
+ *
+ */
 public class Stew {
 	
 	private int numPotatoes;

private-class-data/src/main/java/com/iluwatar/StewData.java

@@ -1,5 +1,10 @@
 package com.iluwatar;
 
+/**
+ * 
+ * Stew ingredients
+ *
+ */
 public class StewData {
 
 	private int numPotatoes;