Interview-GirishRevankar

java/src/main/java/com/elsevier/education/Exercise1.java

@@ -9,34 +9,39 @@
 */
 public class Exercise1 {
 
-	public static class Person {
+	final public static class Person {
 
-		private Set<String> phoneNumbers;
-		private String firstName;
-		private String lastName;
+		//make data members final private so that it can not be changed outside constructor.
+		final private Set<String> phoneNumbers;
+		final private String firstName;
+		final private String lastName;
 
-		public Person() {
+		public Person(Set<String> phonenumbers, String firstname, String lastname) {
+			this.firstName=firstname;
+			this.lastName=lastName;
+			this.phoneNumber=phonenumbers.clone();
 		}
 
 		public Set<String> getPhoneNumbers() {
-			return phoneNumbers;
+			return phoneNumbers.clone();
 		}
-		public void setPhoneNumbers(Set<String> newPhoneNumbers) {
+		//remove all setter methods
+		/*public void setPhoneNumbers(Set<String> newPhoneNumbers) {
 			phoneNumbers = newPhoneNumbers;
-		}
+		}*/
 
 		public String getFirstName() {
 			return firstName;
 		}
-		public void setFirstName(String newName) {
+		/*public void setFirstName(String newName) {
 			firstName = newName;
-		}
+		}*/
 
 		public String getLastName() {
 			return lastName;
 		}
-		public void setLastName(String newName) {
+		/*public void setLastName(String newName) {
 			lastName = newName;
-		}
+		}*/
 	}
-}
+}

java/src/main/java/com/elsevier/education/Exercise2.java

@@ -11,19 +11,41 @@ public class Exercise2 {
 
 	public static class Car {
 
-		private GasEngine engine = new GasEngine();
+		private Engine engine;
 
-		public Car() {
+		public Car(Engine engine) {
+			this.engine=engine;
+		}
+
+		public void setEngine(Engine engine){
+			this.engine=engine;
 		}
 
 		public void moveForward() {
 			engine.spinWheels();
 		}
 	}
 
-	public static class GasEngine {
+	public static class Engine {
+		public abstract void startEngine();
+		public abstract void changeGear();
+		public abstract void spinWheels();
+	}
+
+	public static class GasEngine extends Engine{
 		public void spinWheels() {
 			// no-op for now
+
+			startEngine();
+			changeGear();
+		}
+
+	}
+	public static class ElectricEngine extends Engine{
+
+		public void spinWheels(){
+			startEngine();
+			changeGear();
 		}
 	}
-}
+}

java/src/main/java/com/elsevier/education/Exercise3.java

@@ -20,6 +20,7 @@ public Person(int newId) {
 			id = newId;
 		}
 
+		//your are returning different hashcode for same object everytime.
 		public int hashCode() {
 			return id * generator.nextInt();
 		}
@@ -28,4 +29,4 @@ public boolean equals(Object other) {
 			return id.equals(((Person)other).id);
 		}
 	}
-}
+}

java/src/main/java/com/elsevier/education/Exercise4.java

@@ -11,6 +11,9 @@ public static class Counter {
 
 		private int count = 0;
 
+		//this method need to synchronize as two thread can simultaneously access the count. one can be updating and other might read
+		//giving inconsistence results.
+
 		public int increment() {
 			return ++count;
 		}
@@ -19,9 +22,12 @@ public int getCount() {
 			return count;
 		}
 
+		//this method need to synchronize as two thread can simultaneously access the count. one can be updating and other might read
+		//giving inconsistence results.
+
 		public void resetCount() {
 			count = 0;
 		}
 
 	}
-}
+}

java/src/main/java/com/elsevier/education/Exercise5.java

@@ -8,13 +8,25 @@
 public class Exercise5 {
 
 	public static class Singleton {
+		private static Singleton instance=null;
+
+		protected Singleton(){
+		}
+
+		public static Singleton getInstance(){
+			if (instance == null)
+				instance=new Singleton();
+
+			return instance;
+		}
+
 		public void doSomething() {
 			System.out.println("Doing something....");
 	    }
 	}
 
 	public static void main(String a[]){
-		Singleton st = new Singleton();
+		Singleton st = Singleton.getInstance();
 		st.doSomeThing();
 	}
 }