Shallow clone: if original object's value is changed, and the copy of that object also changes.

this warning message just shows that compiler cannot assure correctness of this casting operation as clone() method returns type of object.

It is really programmer's responsibility to avoid any casting failure.

in this case, a shallow clone will make an extra copy of Vector object. ( only container object is copied)

however, a deep clone will create memory for Vector object and all String objects inside this Vector. ( container and contained objects are all duplicated)