Answer:

mystA sum: 15 mystB sum: 20

The instance variable in mystB did not change.

The trick: the parameter sum of the second method shadowed the instance varaible.

Method Overloading

Overloading is when two or more methods of a class have the same name but have different parameter lists. When a method is called, the correct method is picked by matching the actual parameters in the call to the formal parameter lists of the methods.

Review: another use of the term "overloading" is when an operator calls for different operations depending on its operands. For example + can mean integer addition, floating point addition, or string concatenation depending on its operands.

Say that two processDeposit() methods were needed:

One for ordinary deposits, for which there is no service charge.
One for other deposits, for which there is a service charge.

public class CheckingAccount
{
  . . . .
  private int balance;

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

  public void processDeposit( int amount, int serviceCharge )
  {
    balance = balance + amount - serviceCharge; 
  }

}

The above code implements these requirements. Here is an example main() method that uses both methods:

class CheckingAccountTester
{
  public static void main( String[] args )
  {
    CheckingAccount bobsAccount = new CheckingAccount( "999", "Bob", 100 );
    
    bobsAccount.processDeposit( 200 );       // statement A
    
    bobsAccount.processDeposit( 200, 25 );   // statement B
  }
}

There are two method calls, and two methods to pick from. A method call invokes the method that matches it with both its name and its parameter list.

QUESTION 16:

Examine main().

Which method, processDeposit(int) or processDeposit(int, int) does each statement call?

statement A calls
statement B calls