object - making a class immutable in java

Question

To make a class immutable what I can do is:

1)Make class final
2)do not provide setters
3)mark all variables as final

But if my class has another object of some other class then , somone can change value of that object

class MyClass{
 final int a;
 final OtherClass other 

 MyClass(int a ,OtherClass other){
  this.a = a;
  this.other = other;
 }

 int getA(){
   return a;
 }

 OtherClass getOther(){
   return other;
 }

 public static void main(String ags[]){
  MyClass m = new Myclass(1,new OtherClass);
  Other o = m.getOther();
  o.setSomething(xyz) ; //This is the problem ,How to prevent this?

}
}

Answer 1

A) Make the OtherClass immutable as well

or

B) Don't allow direct access to the OtherClass object, instead providing only getters to act as a proxy.

Edit to add: You could make a deep copy of OtherClass and return a copy rather than the original, but that generally isn't the type of behavior you would expect in Java.