1. 242-210 Programming Fundamentals 2: Interaction/4 1 242-210 F II Objectives – –introduce modularization and abstraction – –explain how an object uses other objects – –compare object and primitive types Semester 2, 2012-2013 4. Object Interaction Original Slides by Dr. Andrew Davison

2. 242-210 Programming Fundamentals 2: Interaction/4 2 Topics 1. Modularization and Abstraction 2. A Digital Clock 3. Using ClockDisplay 4. A More Graphical Clock

3. 242-210 Programming Fundamentals 2: Interaction/4 3 1. Modularization and Abstraction Modularization divides a problem into simpler sub-parts, which can be built separately, and which interact in simple ways. Abstraction is the ability to ignore low level details of a problem to focus on the higher levels.

4. 242-210 Programming Fundamentals 2: Interaction/4 4 Use in Programming Use modularization to split a programming problem into sub-parts (modules). Use modularization to split a programming problem into sub-parts (modules). –implement the modules The implementation of the complete program will be easier, since abstraction can be used to write software in terms of the modules. The implementation of the complete program will be easier, since abstraction can be used to write software in terms of the modules.

5. 242-210 Programming Fundamentals 2: Interaction/4 5 e.g. Robot Software Modules ("black boxes") Abstraction "links" the modules together using their visible interfaces.

6. 242-210 Programming Fundamentals 2: Interaction/4 6 Use in OOP Use modularization to split a programming problem into objects. Use modularization to split a programming problem into objects. Implement the classes for the objects. Implement the classes for the objects. The implementation of the class for the complete program will be easier, since abstraction can be used to write the class in terms of other classes (yours and predefined ones). The implementation of the class for the complete program will be easier, since abstraction can be used to write the class in terms of other classes (yours and predefined ones).

7. 242-210 Programming Fundamentals 2: Interaction/4 7 e.g. Airport Control System Classes for: Plane, Gate, Luggage, Passenger, etc. Use them to create objects such as plane1, plane2, gate2, myLuggage Abstraction simplifies the communication between the objects; only use their visible interface.

8. 242-210 Programming Fundamentals 2: Interaction/4 8 2. A Digital Clock Implement a digital clock display, which shows the hours (0-23) and minutes (0-59).

9. 242-210 Programming Fundamentals 2: Interaction/4 9 Modularizing the Clock Display Divide the clock display problem into two parts Divide the clock display problem into two parts –how to display the hours –how to display the minutes We need two number display objects We need two number display objects We need a NumberDisplay class We need a NumberDisplay class two NumberDisplay objects

10. 242-210 Programming Fundamentals 2: Interaction/4 10 Objects Diagram ClockDisplay object NumberDisplay object (for hours) NumberDisplay object (for minutes)

11. 242-210 Programming Fundamentals 2: Interaction/4 11 NumberDisplay Interface What kind of interface is needed for a NumberDisplay class? What kind of interface is needed for a NumberDisplay class? –get and set the number –return the number as a string useful for printing useful for printing –increment the number the number will 'loop' the number will 'loop' e.g. 0, 1, 2,..., 59, 0, 1,... for the minutes display e.g. 0, 1, 2,..., 59, 0, 1,... for the minutes display

12. 242-210 Programming Fundamentals 2: Interaction/4 12 The NumberDisplay Class public class NumberDisplay { private int currValue; private int currValue; private int maxValue; // number at which currValue goes back to 0 private int maxValue; // number at which currValue goes back to 0 public NumberDisplay(int max) public NumberDisplay(int max) { maxValue = max; { maxValue = max; currValue = 0; currValue = 0; } continued

13. 242-210 Programming Fundamentals 2: Interaction/4 13 public void setValue(int newValue) public void setValue(int newValue) /* Set currValue to the new value. If the new value is less than zero or over maxValue, don't set it. /* Set currValue to the new value. If the new value is less than zero or over maxValue, don't set it. */ */ { if ((newValue >= 0) && (newValue = 0) && (newValue < maxValue)) currValue = newValue; currValue = newValue; } public int getValue() public int getValue() { return currValue; } { return currValue; } continued

14. 242-210 Programming Fundamentals 2: Interaction/4 14 public String getDisplayValue() public String getDisplayValue() // return currValue as a string // return currValue as a string { if (currValue < 10) if (currValue < 10) return "0" + currValue; //pad string with leading 0 return "0" + currValue; //pad string with leading 0 else else return "" + currValue; return "" + currValue; } public void increment() public void increment() /* Increment currValue, rolling over to zero if the /* Increment currValue, rolling over to zero if the maxValue is reached. */ maxValue is reached. */ { currValue = (currValue + 1) % maxValue; } { currValue = (currValue + 1) % maxValue; } } // end of NumberDisplay class

15. 242-210 Programming Fundamentals 2: Interaction/4 15 ClockDisplay Interface What kind of interface is needed for a ClockDisplay class? What kind of interface is needed for a ClockDisplay class? –initialize the clock and set the time –return the current time as a string useful for printing useful for printing –increment the time by one minute The time will be represented using two NumberDisplay fields. The time will be represented using two NumberDisplay fields.

16. 242-210 Programming Fundamentals 2: Interaction/4 16 The ClockDisplay Class public class ClockDisplay { private NumberDisplay hours; private NumberDisplay hours; private NumberDisplay minutes; private NumberDisplay minutes; private String currTimeString; // the current time as a string private String currTimeString; // the current time as a string public ClockDisplay() public ClockDisplay() // intialize the clock to 00:00 // intialize the clock to 00:00 { hours = new NumberDisplay(24); hours = new NumberDisplay(24); minutes = new NumberDisplay(60); minutes = new NumberDisplay(60); setTimeString(); setTimeString(); } two private NumberDisplay fields create two NumberDisplay objects continued

17. 242-210 Programming Fundamentals 2: Interaction/4 17 private void setTimeString() private void setTimeString() /* store the current time as a string of the form "hours:minutes" */ /* store the current time as a string of the form "hours:minutes" */ { currTimeString = hours.getDisplayValue() + ":" + minutes.getDisplayValue(); } { currTimeString = hours.getDisplayValue() + ":" + minutes.getDisplayValue(); } a private method is one that only other methods in the class can call continued method calling in NumberDisplay objects

18. 242-210 Programming Fundamentals 2: Interaction/4 18 public void setTime(int hour, int minute) public void setTime(int hour, int minute) // set time to the specified hour and minute // set time to the specified hour and minute { hours.setValue(hour); hours.setValue(hour); minutes.setValue(minute); minutes.setValue(minute); setTimeString(); setTimeString(); } // end of setTime() } // end of setTime() public String getTime() public String getTime() // return the current time as a string // return the current time as a string { return currTimeString; } { return currTimeString; } continued method calling in NumberDisplay objects

19. 242-210 Programming Fundamentals 2: Interaction/4 19 public void minIncrement() public void minIncrement() // increment the clock by one minute; // increment the clock by one minute; // hour increments when minutes roll over to 0 // hour increments when minutes roll over to 0 { minutes.increment(); minutes.increment(); if (minutes.getValue() == 0) // mins rolled if (minutes.getValue() == 0) // mins rolled hours.increment(); hours.increment(); setTimeString(); setTimeString(); } // end of minIncrement() } // end of minIncrement() } // end of ClockDisplay class

20. 242-210 Programming Fundamentals 2: Interaction/4 20 Classes Diagram uses

21. 242-210 Programming Fundamentals 2: Interaction/4 21 3. Using ClockDisplay public class ClockDemo { public static void main(String[] args) public static void main(String[] args) { ClockDisplay clock = new ClockDisplay(); ClockDisplay clock = new ClockDisplay(); clock.setTime(14, 10); // set time to 14:10 clock.setTime(14, 10); // set time to 14:10 while(true) { while(true) { clock.minIncrement(); clock.minIncrement(); System.out.println(" tick..."); System.out.println(" tick..."); System.out.println("Current time: "+clock.getTime()); System.out.println("Current time: "+clock.getTime()); wait(100); // slow down the looping wait(100); // slow down the looping } } // end of main() } // end of main()

22. 242-210 Programming Fundamentals 2: Interaction/4 22 private static void wait(int milliseconds) private static void wait(int milliseconds) /* stop execution for milliseconds amount of time */ /* stop execution for milliseconds amount of time */ { try { try { Thread.sleep(milliseconds); Thread.sleep(milliseconds); } catch (Exception e) { } catch (Exception e) { } } // end of wait() } // end of wait() } // end of ClockDemo class sleep() is a method in Java's Thread class wait() is a static method so it can be called by main() without main() having to create an object first.

23. 242-210 Programming Fundamentals 2: Interaction/4 23 Compilation and Execution $ javac *.java Compile NumberDisplay.java, ClockDisplay.java, and ClockDemo.java I typed ctrl-c to stop the looping.

24. 242-210 Programming Fundamentals 2: Interaction/4 24 Objects Diagram for ClocksDemo hours minutes currTimeString clock ClockDisplay object currValue maxValue NumberDisplay object 24 14 currValue maxValue NumberDisplay object 60 19 14:19 String object

25. 242-210 Programming Fundamentals 2: Interaction/4 25 4. A More Graphical Clock Michael Kölling and Bruce Quig have developed a simple Canvas class for displaying text and basic shapes in a window. Michael Kölling and Bruce Quig have developed a simple Canvas class for displaying text and basic shapes in a window. We can use Canvas to display the changing clock display instead of using stdout. We can use Canvas to display the changing clock display instead of using stdout.

26. 242-210 Programming Fundamentals 2: Interaction/4 26 Canvas Class Diagram Only showing the public methods (the interface). To use Canvas, we only need to understand its interface. I don't care how it is implemented.

27. 242-210 Programming Fundamentals 2: Interaction/4 27 ClockCanvasDemo public class ClockCanvasDemo { public static void main(String[] args) public static void main(String[] args) { Canvas canvas = new Canvas("Clock Demo",300,150, Color.white); Canvas canvas = new Canvas("Clock Demo",300,150, Color.white); canvas.setVisible(true); canvas.setVisible(true); canvas.setFont( new Font("Dialog", Font.PLAIN, 96)); canvas.setFont( new Font("Dialog", Font.PLAIN, 96)); ClockDisplay clock = new ClockDisplay(); ClockDisplay clock = new ClockDisplay(); clock.setTime(14, 10); // set time to 14:10 clock.setTime(14, 10); // set time to 14:10 while(true) { while(true) { clock.minIncrement(); clock.minIncrement(); canvas.erase(); // clear the canvas canvas.erase(); // clear the canvas canvas.drawString( clock.getTime(), 30, 100); canvas.drawString( clock.getTime(), 30, 100); canvas.wait(100); // slow down the looping canvas.wait(100); // slow down the looping } } // end of main() } // end of main() } // end of ClockCanvasDemo class Using Canvas (compare to slide 21)

28. 242-210 Programming Fundamentals 2: Interaction/4 28 Compilation and Execution $ javac *.java $ java ClockCanvasDemo Compilation includes ClockCanvasDemo.java and Canvas.java