#502 Replaced usages of System.out with logger.

null-object/src/main/java/com/iluwatar/nullobject/NodeImpl.java

@@ -22,6 +22,9 @@
  */
 package com.iluwatar.nullobject;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 /**
  * 
  * Implementation for binary tree's normal nodes.
@@ -29,6 +32,8 @@ package com.iluwatar.nullobject;
  */
 public class NodeImpl implements Node {
 
+  private static final Logger LOGGER = LoggerFactory.getLogger(NodeImpl.class);
+
   private final String name;
   private final Node left;
   private final Node right;
@@ -64,7 +69,7 @@ public class NodeImpl implements Node {
 
   @Override
   public void walk() {
-    System.out.println(name);
+    LOGGER.info(name);
     if (left.getTreeSize() > 0) {
       left.walk();
     }