Question

As in the subject: Is equals() affects vector add() remove() methods behaviour.

I have got Vector<T> v;

1.Does the remove() method will work correct if I will not redefine equals() or hashCode() function in type T?

2.Does the add() method will work correct if I will not redefine equals() or hashCode() function in type T?

Answer 1

1. If you do not define an equals() for T, Vector.remove will use the default equals() implementation, which is object identity (==).
2. Vector.add() does not use equals(). It will happily add duplicates.

In either case, Vector does not use hashCode at all, so the implementation of hashCode (or lack thereof) will not affect the operation of Vector at all. However, if you redefine equals() for your element type, you must redefine hashCode() for other collection structures to work properly.

P.S. You should probably be using ArrayList instead of Vector. From the docs for Vector:

If a thread-safe implementation is not needed, it is recommended to use ArrayList in place of Vector.

Even when a thread-safe implementation is needed, you are usually better off providing your own synchronization. The single-function-call synchronization offered by Vector is usually at the wrong granularity.