Parameters

Here is an example of a method that uses a parameter. (The example is from the CheckingAccount class of the last two chapters.) The ellipses (. . . .) show where code not relevant to this discussion has been left out.

class CheckingAccount
{
  . . . .
  private int    balance;

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

}

The parameter amount is used by a caller send a value to the method. This is usually called passing a value into the method. Here is part of a main() method that uses the parameter to pass a value into the processDeposit() method:

class CheckingAccountTester
{
  public static void main( String[] args )
  {
    CheckingAccount bobsAccount = new CheckingAccount( "999", "Bob", 100 );
    bobsAccount.processDeposit( 200 );

    // . . . . assume that more statements follow
  }
}

When the statement

bobsAccount.processDeposit( 200 );

is executed, the parameter amount of the object's method will hold the value 200. This value is added to the object's instance variable in the statement

balance = balance + amount ; 

Then the method will be exited and control will return to main(). The state of the object referred to by bobsAccount will have been changed.