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Using Classes | page 8 of 11 |
Using the CheckingAccount class is best demonstrated by writing a program that solves a specific problem. We want to study the following scenario:
A interest bearing checking account is created with a balance of $1,000. For two years in a row, add 2.5% interest. How much money is in the account after two years?
Two classes are required: the CheckingAccount class that was developed in the preceding sections, and a second class called CheckingTester . The main method of the CheckingTester class constructs a CheckingAccount object, adds the interest twice, then prints out the balance.
class CheckingTester
{
public static void main( String[] args )
{
CheckingAccount checking =
new CheckingAccount("A123", 1000);
final double INTEREST_RATE = 2.5;
double interest;
interest = checking.getBalance() * INTEREST_RATE / 100;
checking.deposit(interest);
System.out.println("Balance after year 1 is $"
+ checking.getBalance());
interest = account.getBalance() * INTEREST_RATE / 100;
checking.deposit(interest);
System.out.println("Balance after year 2 is $"
+ checking.getBalance());
}
}
The classes can be distributed over multiple files or kept together in a single file. If kept together, the class with the main method must be declared as public . The public attribute cannot be specified for any other class in the same file since a Java source file can contain only one public class.
Care must be taken to ensure that the name of the file matches the name of the public class. For example, a single file containing both the CheckingAccount class and the CheckingTester class must be contained in a file called CheckingTester.java , not CheckingAccount.java .
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