what is Immutable and benefit of Immutable

What is immutable class

         Value of the member variable can’t change once its set

What is the benefit of having immutable?

     As immutable class is read only, it can be used in multi-threading environment without worrying about race condition

        

How to create a class as immutable

   Goal : Create a class, if you have created object for that class, then value should be changed

   Let’s take a class employee

Step 1:  create employee class

  class employee{  
    private int emp_id;  
    private String emp_name;  
    private int emp_age;  
    }  

Problem :  Anyone can declare public function through which can change the value of the variable.

Solution : Declare those variable as final, So that only constructor can assign the value to  the variable

Step 2 : Declare member variable as final

 class employee{  
    private final int emp_id;  
    private final String emp_name;  
    private final int emp_age;  
    public employee (int ID,String NAME , int age){  
        emp_id = ID;  
        emp_name = NAME;  
        emp_age = age;   
     }  
    }  

Remember, if you are passing any object as an input param, then that needs to be deep copied.

Problem : How to retrieve the value of the class

Solution:  Add getter method  , scope is public

Step 3 : Add getter method to retrieve the value

 public int getID(){  
   return emp_id;  
 }  
 public String getName(){  
     return emp_name;  
 }   

        

Step 4 : declare class as final, So that it can’t be inherited

 public final class employee{  
 …  
 …  
 }  

What are the immutable classes available in java ?

         String   class is the best example of the immutable