[anti]

i dont know what it is but im snagged on this problem:

Exercise 2.48: add a further field, refnumber to the book class. this field can store a reference number for a library, for example. it should be a type string and initialized to the zero length string ("") in the constructor as its initial value is not passed in a parameter to the constructor. instead, define a mutator for it with the following signature:

public void setRefNumber (String ref)

the body of this method should assign the value of the paramter to the refNumber field. Add a corresponding getRefNumber accessor to help you check that the mutator works correctly.