Introduction to Classes, Objects, Methods and Strings - Java: How to Program Early Objects - page 86

43 return name; // give value of name back to caller

44 } // end method getName

45 } // end class Account

Fig. 3.8 | Account class with a double instance variable balance and a constructor and
deposit method that perform validation. (Part 2 of 2.)

Account Class Two-Parameter Constructor
The class has a constructor and four methods . It's common for someone opening an account
to deposit money immediately, so the constructor (lines 11-19) now receives a second pa-
rameter— initialBalance of type double that represents the starting balance . Lines 17-18
ensure that initialBalance is greater than 0.0 . If so, initialBalance 's value is assigned to
instance variable balance . Otherwise, balance remains at 0.0 —its default initial value .

Account Class deposit Method
Method deposit (lines 22-26) does not return any data when it completes its task, so its
return type is void . The method receives one parameter named depositAmount —a dou-
ble value that's added to the balance only if the parameter value is valid (i.e., greater than
zero). Line 25 first adds the current balance and depositAmount , forming a temporary
sum which is then assigned to balance , replacing its prior value (recall that addition has a
higher precedence than assignment). It's important to understand that the calculation on
the right side of the assignment operator in line 25 does not modify the balance—that's
why the assignment is necessary.

Account Class getBalance Method
Method getBalance (lines 29-32) allows clients of the class (i.e., other classes whose meth-
ods call the methods of this class) to obtain the value of a particular Account object's bal-
ance . The method specifies return type double and an empty parameter list.

Account 's Methods Can All Use balance
Once again, the statements in lines 18, 25 and 31 use the variable balance even though it
was not declared in any of the methods. We can use balance in these methods because it's
an instance variable of the class.

3.5.2 AccountTest Class to Use Class Account
Class AccountTest (Fig. 3.9) creates two Account objects (lines 9-10) and initializes them
with a valid balance of 50.00 and an invalid balance of -7.53 , respectively—for the pur-
pose of our examples, we assume that balances must be greater than or equal to zero. The
calls to method System.out.printf in lines 13-16 output the account names and bal-
ances, which are obtained by calling each Account 's getName and getBalance methods.

1 // Fig. 3.9: AccountTest.java

2 // Inputting and outputting floating-point numbers with Account objects.

3 import java.util.Scanner;

Fig. 3.9 | Inputting and outputting floating-point numbers with Account objects. (Part 1 of 3.)