How does the "final" keyword in Java work? (I can still modify an object.)

itemprop="text">

In Java we use
final keyword with variables to specify its values are not to
be changed.
But I see that you can change the value in the constructor /
methods of the class. Again, if the variable is static then it
is a compilation error.

Here is the code:

import
            java.util.ArrayList;
import java.util.List;

class Test
            {

 private final List foo;

 public
            Test()
 {
 foo = new ArrayList();
 foo.add("foo"); //
            Modification-1
 }
 public static void main(String[] args)
            
 {
 Test t = new Test();

 t.foo.add("bar"); //
            Modification-2
 System.out.println("print - " + t.foo);

            }
}

Above
code works fine and no errors.

Now change the
variable as
static:

private
            static final List
            foo;

Now it is a
compilation error. How does this final really
work?

Answer

You are always allowed to
initialize a final variable. The compiler
makes sure that you can do it only once.

Note
that calling methods on an object stored in a final variable
has nothing to do with the semantics of final. In other words:
final is only about the reference itself, and not about the
contents of the referenced object.

Java has no
concept of object immutability; this is achieved by carefully designing the object, and
is a far-from-trivial endeavor.