Access Methods

A class with private data provides access to that data through access methods. An access method is a method which uses the private data of its object and is visible to other classes. Some access methods alter data; others return a value but don't alter data. Here is a main() that uses the access methods of a CheckingAccount object.

class CheckingAccount
{
  private String accountNumber;
  private String accountHolder;
  private int    balance;
  . . . .
}

class CheckingAccountTester
{
  public static void main( String[] args )
  {
    CheckingAccount bobsAccount = new CheckingAccount( "999", "Bob", 100 );

    System.out.println( bobsAccount.getBalance() );
    bobsAccount.processDeposit( 200 );
    System.out.println( bobsAccount.getBalance() );

  }
}

This main() program would work with the previous version of the class that did not declare its instance variables to be private. That is because main() uses only access methods with its CheckingAccount object. This is the correct way to use an object. But the previous version of the object could have been used incorrectly. The idea of private is to enforce correct use.

To run this program, copy the CheckingAccount class from the previous page into a file CheckingAccount.java. Then copy the CheckingAccountTester class on this page into a file CheckingAccountTester.java in the same disk directory. Then enter the commands

C:\chap33\> javac CheckingAccount.java CheckingAccountTester.java
C:\chap33\> java CheckingAccountTester

Remember that the name of the file for the java command is the one that contains main() .