Assignment

Implement the calculator of Homework 6 using components rather a monolithic design.

A calculator as four separate components of a display, keypad, accumulator and a calculation unit is a more accurate model of an electronic calculator and is more loosely coupled, the components have no knowledge of the others. The functionality of the Calculator class is realized using components that connect listeners to data sources. 

The calculator consists of the four components: *'ed are provided.

1. *public class Display extends Panel implements PropertyChangeListener
   • graphical object that displays itself
   • PropertyChangeListener listener for a property of type String which is displayed to a TextBox.
      
2. *public class KeyPad extends Panel
   • graphical object which displays itself
   • source of bound property of type String for digits 0..9; property listeners are PropertyChangeListener
   • source of a property of type String for operations +, -, =, etc.; property listeners are OperationListener
   • constructs the keypad with digits 0..9 and operations such as +, -, etc.
   • when 0..9 key is clicked, PropertyChangeListener's are notified
   • when +, =, -, etc. key is clicked, OperationListener's are notified
      
3. public class Accumulator implements PropertyChangeListener, ResetListener

   The function of Accumulator is to listen for and accumulate String digits 0..9 as a double value, "1", "4", "2" would accumulate as: 142.0, for example.  The Accumulator must notify listeners whenever the accumulated value changes and must listen for a reset of the accumulated value to 0.0
    

   • PropertyChangeListener listener for bound property of type String, assumed to be a 0..9 digit
   • ResetListener listener for a Reset, which signals to reset accumulator value to 0.0
   • source of a bound property of type String, the accumulator value; property listeners are PropertyChangeListener.
   • when the accumulator value changes, PropertyChangeListener's are notified
      
4. public class Calculate implements PropertyChangeListener, OperationListener

   Calculate performs calculations much as in Homework 6 by maintaining an accumulator, operand and operation; applying the binary operation to the accumulator and operand whenever an = operation is received (i.e. entering 12+4= yields 16). The function of Calculate then is to listen for and process String operations =, +, -, etc.  and listen for accumulator changes. Calculate must notify listeners whenever the accumulated value changes and notify listeners when to reset (e.g. notify the Accumulator object to reset to 0.0).

   • PropertyChangeListener listener for a bound property of type String, assumed to be one of the operations +, -, =, etc.
   • OperationListener for a property of type String, assumed to be +, -, etc.
   • source of a bound property of type String, Calculate's accumulator value; property listeners are PropertyChangeListener
   • when the accumulator value changes, PropertyChangeListener's are notified
   • source of Reset property, there is no value associated with the property; property listeners are ResetListener
   • ResetListener's are notified whenever they are to reset, such as resetting the Accumulator to 0.0

    

5.  interface OperationListener

   Defines the interface to be implemented by other classes requiring setOperation method.

   public interface OperationListener extends java.util.EventListener {     void setOperation(String operation); }

    

6. interface ResetListener

   Defines the interface to be implemented by other classes requiring resetAccumulator method.

   public interface ResetListener extends java.util.EventListener {     void resetAccumulator(); }

    

The completed Calculator is below, the figure at right illustrates the dataflow between the components.

FILES - Download Homework 11 files.

GETTING STARTED

The provided files consist of completed example of a Calculator having only a KeyPad and Display; the only functionality is to display the digit clicked on the KeyPad to the Display. Note that all graphics is handled by the three classes.

To execute, assuming the path includes the Java bin directory:

javac -classpath . *.java appletviewer Calculator.htm

Use the Calculator.java file listed above along with KeyPad.java, Display.java and any other additional files for the completed assignment.

HINTS

1. Can use the OperationListener and ResetListener as listed above.
2. Use System.out.println to output values to the command window for debugging.
3. Start with Accumulator class, it is the simplest. It connects the KeyPad to the Display objects, useful to test your understanding of bean communication.
4. Remember the difference within a class definition between listening for a property change and notifying listeners of a property change.
   • listening for a property change requires defining:
     • public void propertyChange(PropertyChangeEvent e)
   • notifying listeners of a property change requires defining:
     • public void addxxxxListener(PropertyChangeListener listener) { xxxx.addPropertyChangeListener(listener); }
     • xxxx.firePropertyChange("xxxx", oldValue, newValue);
5. firePropertyChange has no effect when old and new values are the same. Print out the old and new values of firePropertyChange to be certain that the values differ.
6. For simplicity, pass String objects between components using firePropertyChange.

TURN IN

• Cover sheet with your name, date, and Homework 11.
• Printouts of all files you created; at a minimum Accumulator and Calculate.
• Screenshot showing calculator operation.