Our next application (Figs. B.9–B.10) contains a class named
Account (Fig. B.9) that maintains the balance of a bank account. A typical bank services many accounts, each with its own balance, so line 7 declares an instance variable named
balance of type
double. It’s an instance variable because it’s declared in the body of the class but outside the class’s method declarations (lines 10–16, 19–22 and 25–28). Every instance (i.e., object) of class
Account contains its own copy of
1 // Fig. B.9: Account.java 2 // Account class with a constructor to validate and 3 // initialize instance variable balance of type double. 4 5 public class Account ...