Private Methods

A private method of an object can be used only by the other methods of the object. Parts of a program outside of the object cannot directly use a private method of the object.

Say that the bank wants to keep track of how many times each the balance of checking account has been altered. (This might be done as a security measure.) To do this, a use count is added to the data of the CheckingAccount class.

class CheckingAccount
{
  // data-declarations
  private String accountNumber;
  private String accountHolder;
  private int    balance;
  private int    useCount = 0;

  private void incrementUse()
  {
     
  }

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

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

    balance =  balance - amount - charge  ;
  }
  
  // other methods
  . . .
}

The processDeposit() and processCheck() methods call incrementUse() to increment the use count each time they are used. We want the use count to change for these two reasons only, so the incrementUse() method and the variable useCount are made private.