diff --git a/java/src/main/java/com/elsevier/education/Exercise1.java b/java/src/main/java/com/elsevier/education/Exercise1.java
index 90622840..2844d393 100644
--- a/java/src/main/java/com/elsevier/education/Exercise1.java
+++ b/java/src/main/java/com/elsevier/education/Exercise1.java
@@ -9,34 +9,43 @@
 */
 public class Exercise1 {
 
-	public static class Person {
+	//Declare class as final so it cant be extended.
+		public static final class Person {
 		
-		private Set<String> phoneNumbers;
-		private String firstName;
-		private String lastName;
+			//Make mutable fields final so its value can be assigned only once.
+			private final Set<String> phoneNumbers;
+			private final String firstName;
+			private final String lastName;
 		
-		public Person() {
-		}
+			//Initialize the field via constructor
+			public Person(Set<String> phone, String fName, String lName) {
+			this.firstName = fName;
+			this.lastName = lName;
+			set<String> tempSet = new TreeSet<>(phone)
+			phoneNumbers = tempSet;
+			}
 
-		public Set<String> getPhoneNumbers() {
-			return phoneNumbers;
-		}
-		public void setPhoneNumbers(Set<String> newPhoneNumbers) {
+			public Set<String> getPhoneNumbers() {
+				return (Set<String>) ((TreeSet<String>)phoneNumbers).clone();
+			}
+		
+			//no 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) {
 			lastName = newName;
-		}
+		}*/
 	}
 }
\ No newline at end of file
diff --git a/java/src/main/java/com/elsevier/education/Exercise2.java b/java/src/main/java/com/elsevier/education/Exercise2.java
index b7b939e0..102d3c79 100644
--- a/java/src/main/java/com/elsevier/education/Exercise2.java
+++ b/java/src/main/java/com/elsevier/education/Exercise2.java
@@ -11,7 +11,8 @@ public class Exercise2 {
 
 	public static class Car {
 		
-		private GasEngine engine = new GasEngine();
+		@Autowired
+		private GasEngine engine
 		
 		public Car() {
 		}
@@ -21,9 +22,15 @@ public void moveForward() {
 		}
 	}
 	
-	public static class GasEngine {
-		public void spinWheels() {
-			// no-op for now
+	public static abstract class Engine{
+		public  final  void spinWheels(){
+			// TODO Auto-generated method stub
 		}
 	}
+public static class GasEngine extendts Engine {
+		
+	}
+	public static class ElectricEngine extendts Engine {
+		
+	}
 }
\ No newline at end of file
diff --git a/java/src/main/java/com/elsevier/education/Exercise3.java b/java/src/main/java/com/elsevier/education/Exercise3.java
index 6b208652..d82cdd3f 100644
--- a/java/src/main/java/com/elsevier/education/Exercise3.java
+++ b/java/src/main/java/com/elsevier/education/Exercise3.java
@@ -21,7 +21,10 @@ public Person(int newId) {
 		}
 		
 		public int hashCode() {
-			return id * generator.nextInt();
+			final int prime = 31;
+			int result = 1;
+			result = prime * result + ((id == null) ? 0 : id.hashCode());
+			return result;
 		}
 		
 		public boolean equals(Object other) {
diff --git a/java/src/main/java/com/elsevier/education/Exercise4.java b/java/src/main/java/com/elsevier/education/Exercise4.java
index 87ffbc7a..d6f80d87 100644
--- a/java/src/main/java/com/elsevier/education/Exercise4.java
+++ b/java/src/main/java/com/elsevier/education/Exercise4.java
@@ -9,18 +9,23 @@ public class Exercise4 {
 
 	public static class Counter {
 		
-		private int count = 0;
+
+		private AtomicInteger count = new AtomicInteger(0);
+		
+		public Counter(AtomicInteger count) {
+		    this.count = count;
+		}
 		
-		public int increment() {
-			return ++count;
+		public void increment() {
+			count.incrementAndGet();
 		}
 		
-		public int getCount() {
-			return count;
+		public AtomicInteger getCount() {
+			return count;	
 		}
 		
 		public void resetCount() {
-			count = 0;
+			count.set(0);
 		}
 
 	}
diff --git a/java/src/main/java/com/elsevier/education/Exercise5.java b/java/src/main/java/com/elsevier/education/Exercise5.java
index abd81e3f..75a2be8f 100644
--- a/java/src/main/java/com/elsevier/education/Exercise5.java
+++ b/java/src/main/java/com/elsevier/education/Exercise5.java
@@ -8,13 +8,33 @@
 public class Exercise5 {
 	
 	public static class Singleton {
+		
+		//private static variable of the same class
+		private static Singleton myObj;
+		
+		//private Constructor to restrict instantiation from other classes
+		private MySingleton() {		
+		}
+				
 		public void doSomething() {
 			System.out.println("Doing something....");
 	    }
 	}
+	
+	//create static method to get an instance
+	public static MySingleton getInstance(){
+				if(myObj == null){
+					synchronized(MySingleton.class){
+						if(myObj == null){
+		            myObj = new MySingleTon();
+						}
+					}
+				}
+		        return myObj;
+			}
 		
 	public static void main(String a[]){
-		Singleton st = new Singleton();
+		Singleton st = Singleton.getInstance();
 		st.doSomeThing();
 	}
 }