Using Mutable Objects inside user defined Immutable Class

Using Mutable Objects inside user defined Immutable Class

user defined Immutable Class  

We may aware of creating user defined Immutable Class in Java. Basic steps to follow to create immutable class are

• Maintain all member variables and class has defined with final keyword so that variables value can't be modifies and class can't be overridden. 
• Variables values must to set through constructor or through factory pattern.
• Provide only getter methods for member variable. 

In below example lets see simple code which uses mutable object as member variable inside our Immutable class. By returning same original Object in getter which gives loop for user to alter the Objects internal values.

public class Employee {
 private int id;
 private String name;
 private int age;
 
 public Employee(int id, String name, int age) {
  this.age = age;
  this.id = id;
  this.name = name;
 }

 public int getId() {
  return id;
 }
 public void setId(int id) {
  this.id = id;
 }
 public String getName() {
  return name;
 }
 public void setName(String name) {
  this.name = name;
 }
 public int getAge() {
  return age;
 }
 public void setAge(int age) {
  this.age = age;
 } 
}

public final class MyImmutableClass {

 private final int count;
 private final Employee obj;
 
 public MyImmutableClass(int count, Employee obj) {
  this.count = count;
  this.obj = obj;
 }
 public int getCount() {
  return count;
 }
 public Employee getObj() {
  return obj;
 } 
}

public class MyTestClass {

 public static void main(String[] args) {
  
  MyImmutableClass obj1 = new MyImmutableClass(1, new Employee(100, "Steve", 51));
  
  // Here we have created Immutable object for "MyImmutableClass" class
  // Lets see how to change values of mutable object inside Immutable object
  
  obj1.getObj().setName("James");
  
  System.out.println("Count    : "+obj1.getCount());
  System.out.println("Emp ID   : "+obj1.getObj().getId());
  System.out.println("Emp Name : "+obj1.getObj().getName());
  System.out.println("Emp Age  : "+obj1.getObj().getAge());
  
 }
}

OUTPUT:

Count    : 1
Emp ID   : 100
Emp Name : James
Emp Age  : 51

In above example we can see mutable object inside immutable class getting changed. We have created Immutable object with employee name as "Steve" but later same immutable objects value getting changed from "Steve" to "James".
Next we will see how to avoid changing mutable object in Immutable class. For this we need to change 2 things in our above classes 

• In Employee class implements Cloneable and override clone method.
• Next in MyImmutableClass class we need to return clone object instead of original Employee Object. 

Below are the class code changed. 

public class Employee implements Cloneable{
 private int id;
 private String name;
 private int age;
 
 public Employee(int id, String name, int age) {
  this.age = age;
  this.id = id;
  this.name = name;
 }

 public int getId() {
  return id;
 }
 public void setId(int id) {
  this.id = id;
 }
 public String getName() {
  return name;
 }
 public void setName(String name) {
  this.name = name;
 }
 public int getAge() {
  return age;
 }
 public void setAge(int age) {
  this.age = age;
 } 
 
 @Override
 protected Object clone() throws CloneNotSupportedException {
  return super.clone();
 }
}

public final class MyImmutableClass {

 private final int count;
 private final Employee obj;
 
 public MyImmutableClass(int count, Employee obj) {
  this.count = count;
  this.obj = obj;
 }
 public int getCount() {
  return count;
 }
 public Employee getObj() {
  try {
   return (Employee)obj.clone();
  } catch (CloneNotSupportedException e) {
   e.printStackTrace();
  }
  return null;
 } 
}

Next run same code MyTestClass class.

OUTPUT:

Count    : 1
Emp ID   : 100
Emp Name : Steve
Emp Age  : 51

Here we can see even we have changed Employee name from "Steve" to "James" actual object not getting disturbed. 

How to create user defined immutable class in Java?

How to create user defined immutable class in Java?

immutable class  

In this tutorial we will discuss about how to create immutable class in Java. When we say about immutable we will be remembered about important interview question like What is the difference between String and StringBuilder? We are familiar with String is a immutable and StringBuilder is mutable where values once assigned to String variable cannot the changed. 

Yes correct same way this is also interview question as how to create user defined immutable class in Java? Its simple just by Final modifier we can create our own immutable class. For this we need to make class, methods and member variable in the class as Final. By changing the modifier as final one cannot extend the class or override the methods and even cannot change the value once assigned to member variables. By this we can implement our own immutable class.

In below example code will show how to immutable class in Java.

public final class MyImmutableClass {
 
 private final String empName;
 
 public MyImmutableClass(String empName) {
  this.empName = empName;
 }
 
 public String getEmpName(){
  return this.empName;
 }
}

public class TestMyImmutable {
 public static void main(String[] args) {
  MyImmutableClass obj = new MyImmutableClass("Raj");
  
  /* 
   * Values once assigned cannot to changed by using set methods.
   * Just we can get the value assigned to the variable.
  */
  String empName = obj.getEmpName();
  System.out.println("Emp Name : "+empName);  
 }
}