Problem 01 - Ch-13

Author: deepak-malik

src/com/deepak/ctci/Ch13_Java/Problem_01.java

@@ -15,4 +15,55 @@
  */
 public class Problem_01 {
 
+	/* In java, when a class is defined it gets a default public constructor.
+	 * When we talk about inheritance, it allows us to use the properties and methods
+	 * of the other class. The class which is using the properties and method is
+	 * called a sub class whereas the class which actually owns those properties and methods
+	 * is called a super class. 
+	 * For this particular problem, when a constructor is declared as private, 
+	 * it can be accessed by all those classes which can access the private methods
+	 * of the that class. Moreover, a private constructor will not allow the class to
+	 * be instantiated */
+
+	private static Problem_01 obj = null;
+
+	/**
+	 * Private Constructor
+	 */
+	private Problem_01() {}
+
+	/**
+	 * Method to make sure only one instance is created
+	 * @return {@link Problem_01}
+	 */
+	public static Problem_01 objectCreationMethod(){
+		/* This logic will ensure that no more than one object can be created at a time */
+		if(obj == null){
+			obj = new Problem_01();
+		}
+		return obj;
+	}
+
+	/**
+	 * Method to display a message
+	 */
+	public void display(){
+		System.out.println("Singleton class Example");
+	}
+
+	/**
+	 * Main method to test the execution of program
+	 * No unit tests needed
+	 * @param args
+	 */
+	public static void main(String[] args) {
+		/* Creating singleton instance of the class because object cannot
+		 * be created due to the existence of private constructor.
+		 * You can instantiate the class here because this main method
+		 * is inside the Problem_01 class and private methods can be 
+		 * accessed within the class. */
+		Problem_01 singeltonClass = Problem_01.objectCreationMethod();
+		singeltonClass.display();
+	}
+
 }