Null object as a singleton #50

null-object/src/main/java/com/iluwatar/NullNode.java

@@ -1,33 +1,44 @@
-package com.iluwatar;
-
-/**
- * 
- * Null Object implementation for binary tree node.
- *
- */
-public class NullNode implements Node {
-
-	@Override
-	public int getTreeSize() {
-		return 0;
-	}
-
-	@Override
-	public Node getLeft() {
-		return null;
-	}
-
-	@Override
-	public Node getRight() {
-		return null;
-	}
-
-	@Override
-	public String getName() {
-		return null;
-	}
-
-	@Override
-	public void walk() {
-	}
-}
+package com.iluwatar;
+
+/**
+ * 
+ * Null Object implementation for binary tree node.
+ * 
+ * Implemented as Singleton, since all the NullNodes are the same.
+ *
+ */
+public class NullNode implements Node {
+
+	private static NullNode instance = new NullNode();
+	
+	private NullNode() {
+	}
+	
+	public static NullNode getInstance() {
+		return instance;
+	}
+	
+	@Override
+	public int getTreeSize() {
+		return 0;
+	}
+
+	@Override
+	public Node getLeft() {
+		return null;
+	}
+
+	@Override
+	public Node getRight() {
+		return null;
+	}
+
+	@Override
+	public String getName() {
+		return null;
+	}
+
+	@Override
+	public void walk() {
+	}
+}