pls explain about wrapper class

Wrapper class is exactly wrap primitive types (eg: int, double, etc) in Objects which can be placed into Vectors, and many, many other uses

creating wrapper classes

Integer i = Integer.valueOf("125");

the more common use is given the primitive in a variable.

Integer

Integer I = Integer.valueOf(i); //Wrapper
int i2 = I.intValue(); //back to primitive

boolean

boolean b = true;
Boolean B = Boolean.valueOf(b); //Wrapper
boolean b2 = B.booleanValue(); //back to primitive