1. CS 180 Problem Solving and Object Oriented Programming Fall 2010 Notes for Week 11: Nov 1-5, 2010 Aditya Mathur Department of Computer Science Purdue University West Lafayette, IN, USA http://www.cs.purdue.edu/homes/apm/courses/CS180Fall2010/ 1.Q&A 2.Class and instance variables 3.private, public, static 11/1 This Week: 11/3 1.Methods and parameters 2.Inheritance 3.Thread class 4.Concurrency: Task decomposition Data decomposition

2. Readings and Exercises for Week 11 Readings: Method and data hiding: 7.2, 7.3 Class: 8.2, 8.3 Inheritance: 10.2, 10.3 Exercises: 7.1, 7.2, 7.3, 7.4, 7.5, 8.1, 8.2, 8.3 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 2

3. Special Sessions Lab Help: Thursday November 4, 5:30-7:00pm Monday November 11, 5:30-7pm LWSN B158 Project 4 Due: Monday November 15, 2010 Special Class: Sunday November 7, 5-7pm LWSN 3102AB 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 3

4. Lunch meeting When: Thursday November 4, 2010. Noon-1:30pm Where: Ford Dining Hall Meet: Upstairs in the separate dining room Attendees: Please sign up with your recitation instructor or email me by Wednesday November 3 Look forward to seeing you! 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 4

5. Feedback: I liked Android labs. 11/5/2010 (a)A lot (b)Somewhat (c)Not at all ©Aditya Mathur. CS 180. Fall 2010. Week 11 5

6. Feedback: Lab instructors are helpful. 11/5/2010 (a)A lot (b)Somewhat (c)Not at all ©Aditya Mathur. CS 180. Fall 2010. Week 11 6

7. Feedback: So far I am liking the course (10 liking a lot, 1 not liking at all). 11/5/2010 (a)8-10 (b)4-7 (c)1-3 ©Aditya Mathur. CS 180. Fall 2010. Week 11 7

8. End of Feedback: 11/1/2010 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 8

9. Back to Classes, objects, methods! 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 9

10. Review 11/5/2010 Listeners: MenuListener, KeyListener Widgets: JMenuBar, JMenu, JMenuItem Menu events: menuSelected(), menuDeselected(), menuCanceled() Key events: keyPressed(), keyReleased(), keyTyped() getSource() and getKeyChar() ©Aditya Mathur. CS 180. Fall 2010. Week 11 10

11. Dividing work into small segments 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 class Instance variables Class variables Methods class Instance variables Class variables Methods class Instance variables Class variables Methods Program 11

12. Instance variables 11/5/2010 public class Fruit{ public String name; public String color; public int type } ©Aditya Mathur. CS 180. Fall 2010. Week 11 public class Market{ public static void main(String [] args){ System.out.println(Fruit.color); } Will this compile? No: because color is not static 12

13. Instance variables 11/5/2010 public class Fruit{ public String name; public String color=“Red”; public int type; public void changeColor(String c){ color=c; } ©Aditya Mathur. CS 180. Fall 2010. Week 11 public class Market{ public static void main(String [] args){ Fruit apple=new Fruit(); Fruit pear=new Fruit(); pear.changeColor(“Green”); System.out.println(apple.color); System.out.println(pear.color); } Will this compile? Yes because we are accessing instance variables via their objects. 13

14. Class variables 11/5/2010 public class Fruit{ public String name; public static String color; public int type; } ©Aditya Mathur. CS 180. Fall 2010. Week 11 public class Market{ public static void main(Strings[] args){ System.out.println(Fruit.color); } Will this compile? Yes, because color is static and public. 14

15. Class: variables 11/5/2010 public class Fruit{ public String name; public static String color; public int type } ©Aditya Mathur. CS 180. Fall 2010. Week 11 public class Market{ public static void main(Strings[] args){ Fruit apple=new Fruit(); System.out.println(apple.color); } Will this compile? Yes, because color will be obtained from Fruit which is the parent class of apple. 15

16. Private/Public variables 11/5/2010 public class Fruit{ public String name; private String color=“Red”; int type; } ©Aditya Mathur. CS 180. Fall 2010. Week 11 public class Market{ public static void main(String [] args){ Fruit apple=new Fruit(); Fruit pear=new Fruit(); System.out.println(apple.color); System.out.println(pear.color); } Will this compile? No, color is private to the Fruit class. 16

17. Private/Public variables 11/5/2010 public class Fruit{ public String name; private String color=“Red”; int type; public void changeColor(String c){ color=c; } public String getColor(){ return color; } ©Aditya Mathur. CS 180. Fall 2010. Week 11 public class Market{ public static void main(String [] args){ Fruit apple=new Fruit(); Fruit pear=new Fruit(); pear.changeColor(“Green”); System.out.println(apple.getColor()); System.out.println(pear.getColor()); } Will this compile? Yes, because now we are using the public getColor() method to get color. 17

18. Accessor and mutator methods 11/5/2010 public class Fruit{ public String name; private String color=“Red”; int type; public void changeColor(String c){ color=c; } public String get Color(){ return color; } ©Aditya Mathur. CS 180. Fall 2010. Week 11 Accessor method Mutator method 18

19. Accessibility rules: Let us fill this table 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 ModifierClassPackageSubclassWorld publicYYYY privateYNNN noneYYNN 19 If a variable or an object declaration uses this modifier then can this variable or object be used inside ? Package: A collection of classes identified as a Java package. World: Collection of packages Y: Yes. N: No.

20. Local and global variables/objects 11/5/2010 public class X{ public JButton plus; public void doSomething(String c){ int z; for (int i=0; i<10; i++){ int p; } System.out.println(i, p); } // end of method }// end of class ©Aditya Mathur. CS 180. Fall 2010. Week 11 z, c can be use here i can be Used here i, p out of scope plus can be used here 20

21. Methods and parameters 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 21

22. Method [header] declaration 11/5/2010 public int find( JButton [] b, Object o) ©Aditya Mathur. CS 180. Fall 2010. Week 11 22 Method Name (required) Formal Parameters 0 or more Return type (required) (Optional) Access modifier

23. Method call 11/5/2010 public int find( JButton [] b, Object o) ©Aditya Mathur. CS 180. Fall 2010. Week 11 Actual Parameters 23 int index=find( button, source) One-to-one correspondence of formal and actual parameters

24. Parameter types 11/5/2010 Value parameters: That are passed by value. All parameters in Java are passed by value. Reference parameters: Objects and arrays are reference parameters. This means that a reference to an object, not the object itself, is passed to the method. ©Aditya Mathur. CS 180. Fall 2010. Week 11 24

25. Pass by value: value of a primitive type is passed 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 public void test (int x){ x=3; } int p=0; test(p); System.out.println(p); Formal parameter Actual parameter The value of p does not change even though test sets its formal parameter to 3. 25

26. Pass by value: reference to an object is passed 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 public void test (int [] a){ a[0]=15; } Formal parameter int [] b=new int [100]; b[0]=21; test(b); System.out.println(b[0]); Actual parameter The value of b[0] changes to 15 26

27. Pass by value: reference to an object is passed 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 Formal parameter public static void changeString(String [] x){ x[0]="Zero"; x=new String [2]; } public static void main(String [] args){ String [] y=new String [5]; y[0]="Z"; y[1]="O"; System.out.println(y[0]+” “+ y[1]); changeString(y); System.out.println(y[0] +” “+ y[1]); } Actual parameter 27

28. Parameter passing: another example 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 28 public static void test(String [] x, int z){ x[0]="Zero"; // An element changed to "Zero" x=new String [2]; z=100; // z set to 100 } public static void main(String [] args){ String [] y=new String [5]; int p=0; y[0]="Z"; y[1]="O"; System.out.println(p); System.out.println(y[0]+ " "+y[1]); test (y, p); System.out.println(y[0]+ " "+y[1]); System.out.println(p); }

29. Parameter passing: yet another example 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 29 public class PassByRefArray{ static int [] b=new int [100]; public static void test(int [] a){ b=a; a[0]=99; a[1]=299; } public static void main(String [] args){ b[0]=15; System.out.println(b[0]+" "+b[1]); test(b); System.out.println(b[0]+" "+b[1]); } What will be displayed?

30. Method parameters 11/5/2010 public int find( JButton [] b, Object o){ int len=b.length, index=0; boolean found=false; while(!found && index<len){ if(o==b[i]){ found=true; break; } index++; } // end of while if(!found) return (-1); else return (index); } // end of method ©Aditya Mathur. CS 180. Fall 2010. Week 11 Method to find which button was clicked. Returns button index if found else returns a -1. Parameters 30

31. Method parameter: summary 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 A method may have zero or more parameters. Each parameter has a name. Each parameter must have a type Primitive types are passed by value; references to objects are passed and not the object itself Each method must have a return type. Each parameter becomes a local variable for the method. A constructor is a special method that has no return type. 31

32. Inheritance 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 32

33. Inheritance 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 public class Fruit{ public String name; private String color=“Red”; int type; public void changeColor(String c){ Color=c; } public String getColor(){ return color; } public class Mango extends Fruit{ public String origin; public void harvest(){ } public String getOrigin(){ return color; } All methods and local variables/objects are available to Mango. 33

34. Inheritance: Another example 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 public class Gui extends JFrame{ } All methods and local variables/objects of JFrame are available to Gui. 34

35. More on inheritance later! 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 35

36. Concurrent Programming 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 36

37. Concurrency 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 37 TT1T1 T2T2 TNTN.. T Main thread controls the distribution of work N threads executing concurrently to execute N tasks T 1, T 2 …T N. Distribute work Task T is divided into N simpler tasks and executed in parallel

38. Threads 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 Thread is a class A thread is a sequence of computations that can run in parallel with other threads. One uses the Thread class to create a thread. 38

39. Problem 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 Given doubles x and y and a boolean z, write a program to compute the following sin(x)/cos(y)+(x 2 +y 2 ); if z is true sin(x)/cos(y)+(x 2 - y 2 ); if z is false 39

40. Problem: Solution architecture 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 40 T T1T1 T2T2 T T: Perform the given task T 1 : Compute a part of the expression T 2 : Compute a other part of the expression Combine the results of T 1 and T 2 How many threads?

41. Problem: Algorithm 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 Thread A: Input: x and y Compute sin(x)/cos(y) Thread B: Input: x, y, z Compute x 2 +y 2 if z is true or x 2 -y 2 if z is false Thread C (control thread): Input: x, y, z; Create an object e1(Thread A ); Create can object e2(Thread B); Start e1; Start e2; Wait for e1 and e2 to complete; Get value computed by e1; Get value computed by e2; Add the two values and display the result; 41

42. Problem: Program 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 42

43. Week 11: November 1-5, 2010 Hope you enjoyed this week! Questions? Contact your recitation instructor. Make full use of our office hours. 11/5/2010 ©Aditya Mathur. CS 180. Fall 2010. Week 11 43