Implement a final class without the “final” keyword

Question

A friend of mine was asked that question in his on-phone job interview a couple of days a go. I don\'t have a clue. can anyone suggest a solution? (His job interview is ov

Answer 1

public class Immutable {       
    private int val;

    public Immutable(int v)
    { 
        this.val = v;
    }

    public int getVal() { return this.val; }
}

Answer 2

• Mark constructor as private
• Provide a static method on the class to create instance of a class. This will allow you to instantiate objects of that class

Answer 3

Make all the constructors of that class as private to stop inheriting, Though not recommended.

Answer 4

Static classes can't be inherited from

Answer 5

Create a private constructor without parameters?

public class Base
{
    private Base()
    {
    }
}

public class Derived : Base
{
//Cannot access private constructor here error
}

Answer 6

You can make your class immutable without using final keyword as:

1. Make instance variable as private.
2. Make constructor private.
3. Create a factory method which will return the instance of this class.

I am providing immutable class here in Java.

class Immutable {
    private int i;
    private Immutable(int i){
     this.i = i;
    }
    public static Immutable createInstance(int i){
         return new Immutable(i);
    }
    public int getI(){return i;}
}
 class Main {
    public static void main(string args[]){
       Immutable obj = Immutable.createInstance(5);
    }
}