Various classes such as Vector, Stack, etc. are containers for arbitrary members of class
Object
Primitive types, such as
int
float
double
boolean
are not Objects (String's are)
If we wish to use primitive types in containers, we must first "wrap" the value as an Object.
Java (in java.lang) provides a collection of wrappers for this purpose:
Integer wraps int [sic]
Long wraps long
Double wraps double
etc.