List v = new Vector() how can i write this ?

Question

List v = new Vector() how can i write this ?
vector does not 'extends' List rather it 'implements' only ......so how can write this way ? ( polymorphism applies only for 'extends' ).

Answer 1

my question in a simple way is :
List some_list extends Vector
No, List is an interface; Vector is a concrete class. Read the javadocs.
Vector implements List
>
AND
List some_list implements Vector
are these two same in behaviour
our  apart from theoretical differences ?thanks
Interfaces don't have any implementation; they're pure method signatures. When a concrete class implements an interface, it makes a promise that says "I will provide implementations for exactly these methods. Any client can call a method from the interface and I will do something 'sensible' if I'm written correctly."
From the point of view of static and dynamic types, there's no difference between interfaces and classes.
C++ has interfaces, too - they're classes with all pure virtual methods. If you understand how C++ works, the concept shouldn't be hard.
ArrayList is preferred precisely because it isn't synchronized by default. (You can always make it so using java.util.Collections if you wish later on.) If you don't need synchronization, why pay the performance penalty?