added visitor pattern sample

visitor/src/main/java/com/iluwatar/SergeantVisitor.java

@@ -0,0 +1,22 @@
+package com.iluwatar;
+
+public class SergeantVisitor implements UnitVisitor {
+
+	@Override
+	public void visitSoldier(Soldier soldier) {
+		// TODO Auto-generated method stub
+
+	}
+
+	@Override
+	public void visitSergeant(Sergeant sergeant) {
+		System.out.println("Hello " + sergeant);
+	}
+
+	@Override
+	public void visitCommander(Commander commander) {
+		// TODO Auto-generated method stub
+
+	}
+
+}