Private Methods

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  ;
  }
}

A private method is one that can be used only by the other methods of an object. Parts of a program outside of the object cannot directly invoke (use) a private method of the object.

Say that the bank wants to keep track of how many times each checking account is used. (This might be done as a security measure.) A "use" of the checking account is processing a deposit or a check. To do this, a "use count" is added to the data of the CheckingAccount class (some parts of the class have been temporarily left out).

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