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

package com.iluwatar.nullobject;

/**
 * 
 * Null Object pattern replaces null values with neutral objects.
 * Many times this simplifies algorithms since no extra null checks
 * are needed.
 * <p>
 * In this example we build a binary tree where the nodes are either
 * normal or Null Objects. No null values are used in the tree making
 * the traversal easy.
 *
 */
public class App 
{
	/**
	 * Program entry point
	 * @param args command line args
	 */
    public static void main( String[] args ) {
    	
    	Node root = new NodeImpl("1",
    			new NodeImpl("11",
    					new NodeImpl("111",
    							NullNode.getInstance(),
    							NullNode.getInstance()),
    					NullNode.getInstance()), 
    			new NodeImpl("12",
    					NullNode.getInstance(),
    					new NodeImpl("122",
    							NullNode.getInstance(),
    							NullNode.getInstance())));

    	root.walk();
    }
}