The `private` Visibility Modifier

When an instance variable is declared private it can be used only by the methods of that class. Here is the checking account class definition from the last chapter with each of its variables declared to be private.

Now only the methods of a CheckingAccount object can "see" accountNumber, accountHolder, and balance. There is no change in these methods because their access to the instance variables is the same as before.

class CheckingAccount
{
  // variable declarations
  private String accountNumber;
  private String accountHolder;
  private int    balance;

  //constructor
  CheckingAccount( String accNumber, String holder, int start )
  {
    accountNumber = accNumber ;
    accountHolder = holder ;
    balance       = start ;
  }

  // methods
  int getBalance()
  {
    return balance ;
  }

  void  processDeposit( int amount )
  {
    balance = balance + amount ; 
  }

  void processCheck( int amount )
  {
    int charge;
    if ( balance < 100000 )
      charge = 15; 
    else
      charge = 0;

    balance =  balance - amount - charge  ;
  }

}

QUESTION 2:

The balance can no longer be changed outside of the object with an assignment statement. How can you change the balance in a CheckingAccount object?

Answer:

The private Visibility Modifier

QUESTION 2:

The `private` Visibility Modifier