CS#180#Problem#Solving#and#ObjectOriented# …# name:# “Mango”# color:Yellow price:3.99#...

CS 180 Problem Solving and Object Oriented Programming Fall 2011

Notes for Week 12: Nov 7-‐11, 2011

Aditya Mathur Department of Computer Science Purdue University West LafayeLe, IN, USA

hLp://www.cs.purdue.edu/homes/apm/courses/CS180Fall2011/

This Week:

11/7-‐11 1.  Quiz 2.  Review 3.  Concurrent programming 4.  Concurrent linear search 5.  CHALLENGE PROBLEM 6.  Concurrent bubble sort and

merge

Readings and Exercises for Week 12 [Prepara_on for Exam 2]

Readings: Chapters: 2, 3, 4, 5, 7, 8, 1, and 19 No ques_ons on: Interfaces, inheritance, JOp_onPane, images, sounds, applets

Focus

Exercises:

Exam 2 Prac_ce Problem Set [available via the course web site] ©Aditya Mathur. CS 180. Fall 2011. Week 12

File input (Scanner)/output (PrintWriter); Arrays: single and mul_dimensional; GUIs (with Ac_on and Mouse Listeners; Grid and Border layouts).

Exam 2

When: Wednesday November 9, 2011; 8-‐10pm.

Where: WTHR 200

Format: Open book [Any one book on Java]

Two programming problems.

Problem 1: Arrays/Files

Problem 2: GUIs

©Aditya Mathur. CS 180. Fall 2011. Week 12

BRING YOUR ID!

Project 4

To type password so that characters do not show, use, but

only if you wish to,

JPasswordField pass=new JPasswordField ()

instead of JTextField().


Quiz


1.  Names of formal and actual parameters must be the same

A True

B. False


2. Types of formal and actual parameters must be the same or conver_ble.

A True

B. False


3. One of the following is incorrect. Which one.?

A. JPanel p=new JPanel();

B.  JFrame f= new JFrame(“Is this OK?”);

C.  JPanel p= new JPanel(new GridLayout(3, 4)); D.  JFrame f= new JFrame(new GridLayout(3, 4);


4. One of the following is incorrect. Which one?

A.  int [][] a=new int[][4]; B.  int [][] a=new int[100][4]; C.  int [][] a=new int[3][4]; D.  int [][] a=new int[100][0];


5. Default layout for a JPanel is

A.  GridLayout B.  FlowLayout C.  BorderLayout D.  BoxLayout


6. When transferring actual parameters to a method the following is passed

A.  Value of the actual parameter

B.  Reference to the actual parameter

C.  None of the above


7. A constructor is always required.

A.  True B.  False


8. There can be more than one constructor in a class defini_on.



9. A non-‐sta_c method in a class can directly call a sta_c method in that class.



10. A sta_c method in a class can directly call a non-‐sta_c method in that class.



Review: Files


File object

•  File f; // declares an object of type File

•  File f=new File (“data.txt”); // Create a File object

•  String filename=“data.txt”;

File f=new File (fileName); // Create a File object

•  Full pathnames can be specified when crea_ng a File

object.


File Input


Scanner inFile=new Scanner(f); // Creates a Scanner for data.txt

•  Must be inside try-‐catch.

•  boolean b= inFile.hasNext();// Checks if there is more data to be input

String s=inFile.next(); // Read a string

•  int num=inFile.nextInt(); // Read an int

•  double num=inFile.nextDouble(); // Read a double


File Output


PrintWriter outFile=new PrintWriter(f); // Creates a writer for data.txt

•  Must be inside try-‐catch.

•  outFile.print(d); // Write d in to the file; d may be any primi_ve type,

// string, or even an arbitrary object.

•  outFile.println(d); // Same as print() but terminates line.

•  outFile.prinq(format, d); // Same as print but formaLed

•  outFile.close();// Needed to ensure all data is flushed to the file.


Review: Arrays


Arrays of primi_ve types

•  int [] a; // Declare an array

•  int [] a=new int [n]; // Create an array

•  long [][] x; // Declare an array

•  long [][] x=new long [10][]; // Create an array

•  long [][]x=new long [10][5]; // Create an array


Array of primi_ve types: Visual int [] a=new int [3]; // Create an array


0

1

2

0

0

0

a

a[0]=5; 0

1

2

5

0

0

a

Arrays of objects •  JBuLon [] b; •  JBuLon [] b=new JBuLon[n];


Array of objects: Visual JBuLon [] b=new JBuLon[3];


0

1

2

null

null

null

b

Array of objects: Null pointer excep_on JBuLon [] b=new JBuLon[3];


0

1

2

null

null

null

b

buLon[0].setText("Hello");

What happens if we do the following?

Array of objects: Crea_ng an object JBuLon [] b=new JBuLon[3] b[0]=new JBuLon(“Hello”);


0

1

2

null

null

b Hello

Array of objects: Modifying an object JBuLon [] b=new JBuLon[3] b[0]=new JBuLon(“Hello”);


b[0].setText(”Hi!");

What happens if we do the following?

0

1

2

null

null

b Hi!

Array of objects: Another example

Fruit [] f=new Fruit[3]


f[0].setFruitColor(Color.Yellow); f[0].setPrice(3.99);

0

1

2

null

null

f null

f[0]=new Fruit(“Mango”); 0

1

2

null

null

f

name: “Mango” color: price:

name: “Mango” color: Yellow price:3.99

Review: Methods


Method header


Modifier public/ private/ none

Modifier sta_c/ none

Return type

Name Parameters 0 or more

public boolean find(int [] a, int x)

Method parameters


public boolean find(int [] a, int x)

Value parameter

Reference parameter

Value parameter: primi_ve types

Reference parameter: objects

Value parameters


public boolean find(int [] a, int x){

System.out.println(x); x++;

}

int y=15; int[] num={2, 3, 15, -‐29}; boolean found=find(num, y) System.out.println(found + ” “+ y);

What is displayed?

Value of actual parameter is passed

Reference parameters


public boolean find(int [] a, int x){ System.out.println(a[1]); x++; a[1]++;

}

int y=15; int [] num={2, 3, 15, -‐29}; boolean found=find(num, y) System.out.println(found + ” “+ num[1]);

What is displayed?

Reference to actual parameter is passed

The main() method


public sta_c void main(String [] args){

}

Is this value or a reference parameter?

How can we pass parameters to the main() method?

Method parameter: summary


•  A method may have zero or more parameters.

•  Each parameter has a name.

•  Each parameter must have a type

•  All parameters are passed by value. For primi_ve types the value of the actual parameter is passed. For reference types a reference to the object is passed.

•  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.

Review: Class and instance variables


Class and instance variables


public class Home{ public sta_c String measureUnit=“Square Feet”; public sta_c String code=“Pub. L. 110-‐140”; private String address=“”; private int bedRooms=4; public Home(String a, int r){

address=a; bedRooms=r; }

public int getBedrooms(){ return(bedRooms);

}

Class variables

Instance variables

Class and instance variables


Home h1=new Home(“1400 X Street”, 4); address=“1400 X Street” bedRooms=4

Home h2=new Home(“1500 Y Street”, 3);

address=“1500 Y Street” bedRooms=3

System.out.println(Home.getBedRooms());

System.out.println(h2.getBedRooms());

System.out.println(h1.code);

System.out.println(h2.code);

System.out.println(h1.getBedRooms());

h1

h2

System.out.println(Home.code);

Class variables


Declared using the sta_c keyword.

Not a part of the object, but part of the class in which they are declared.

Accessible via the objects created from that class

Declare a variable or a method as sta_c only if does not depend on the object.

Instance variables


Declared without using the sta_c keyword

Part of an object

Accessible via the objects created from the parent class

Declare a variable as an instance variable if its value depends on the object.

The main() method


Is declared to be sta_c

Can it access instance variables in its parent class?

What variables and methods in the parent class can the main method access?

Accessibility rules


Modifier Class Package Subclass World

public Y Y Y Y

private Y N N N

none Y Y N N

If a variable or an object declara_on uses this modifier

then can this variable or object be used inside ?

Package: A collec_on of classes iden_fied as a Java package. World: Collec_on of packages

Y: Yes. N: No.

Review: Local and global variables


Local variables


public void test(int x){ int p, q; }

x, p, q are local to method test. test is public and hence global and can be used in all classes. Variables and objects declared inside a method are local to that method.

Local variables: Use of public and private modifiers


public void test(int x){ int p, q; public int z; }

x, p, q are local to method test. test is public and hence global and can be used in all classes. Declara_ons inside a method cannot be preceded by public or private.

Global variables


public class Toy{ public String name; private String owner; }

name is global as it is declared to be public. Owner is local to this class Toy is global and can be used anywhere.

Local and global variables: Example public class X{ public JBuLon 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


z, c can be use here

i can be Used here

i, p out of scope

plus can be used here

Review: Inheritance


Inheritance


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.

Inheritance: Another example


public class Gui extends JFrame{ }

All methods and local variables/objects of JFrame are available to Gui.

Review: GUI


GUI: Widget/Methods


JFrame JPanel JBuLon JTextField JMenuBar JMenu JMenuItem

setSize() setVisible( ) setText() getText add()

GUI: Listeners/Methods


Ac_onListener MenuListener KeyListener MouseListener

getSource() addAc_onListener()

GUI: Interface


A class implements an interface All methods in the interface must be implemented. Ac_onListener is an interface.

GUI: Abstract Class


Similar to interface but may implement some methods thus avoiding the need to implement all methods. MouseAdapter is an abstract class.

Announcements


•  No Feast With Faculty tonight due to Exam 2.

•  Project 5 will be assigned this Friday, earlier than adver_sed, but the due date will not change.

•  I will be out of the country next week.

•  On Nov 14/16 Suleyman Cen_nas will solve problems related to concurrent programming. Please aLend!

•  Exam 2 TODAY! WTHR 200. 8pm.

Concurrent Programming


Dividing work into small segments


class

Instance variables Class variables Methods

class


class


Program

Concurrency


T

T1 T2 TN . . . .

T

Main thread controls the distribu_on of work

N threads execu_ng concurrently to execute N tasks T1, T2…TN.

Distribute work

Task T is divided into N simpler tasks and executed in parallel

Threads


•  Thread is a class

•  A thread is a sequence of computa_ons that can run in parallel with other threads.

•  One uses the Thread class to create a thread.

Problem


•  Given doubles x and y and a boolean z, write a program to compute the following

sin(x)/cos(y)+(x2+y2); if z is true sin(x)/cos(y)+(x2 -‐ y2); if z is false

Problem: Solu_on architecture


T

T1 T2

T

T: Perform the given task

T1: Compute a part of the expression

T2: Compute a other part of the expression

Combine the results of T1 and T2

How many threads?

Problem: Algorithm


Thread A: Input: x and y

Compute sin(x)/cos(y)

Thread B: Input: x, y, z

Compute x2+y2 if z is true or x2-‐y2 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;

Problem: Program


Back to Concurrency


Thread: What is it?


•  A thread is a sequence of computa_on that can run in

parallel with other threads.

•  Every program has at least one thread of computa_on.

•  Each thread is associated with an instance of the class

Thread.

•  A program with two or more threads is generally referred to

as a mul_threaded program.

•  A mul_threaded program is generally used to speed up the

solu_on to a problem.

Thread: Typical lifecycle


Define class that extends Thread.

Create thread.

Start thread.

Wait for thread to terminate.

Get results from thread.

Use results from thread.

Thread: Defining a class


Thread is a class. One way to create a new thread is to first

define a class that extends the Thread class.

public class Search extends Thread{

String [] x; // For use by a thread

String s; // Another object for use by the thread

int tID; // Thread ID if needed

int start, end; // Start and end indices for search

boolean found; // Computed by the thread

}

Thread: The constructor


A class that extends Thread generally has a constructor that is

used to pass parameters to a thread as follows.

public Search (String [] a, String s, int start, int end, int tID, ){

// Save parameters for use when the thread executes

x=a;

this.s=s; this.start=start; this.end=end;

this.tID=tID

}

Thread: The run() method


Unlike the main() method, every thread object created from

Thread must have a run() method.

When a thread is started, its execu_on begins in the run()

method and terminates when the run() method terminates

Thread: The run() method: Example


public void run (){ // Must not have any parameters

// Thread execu_on begins here.

System.out.println(“Hi! I am thread “+tID);

System.out.println(“Bye bye! See you!”);

}

The run() method does not take any parameters. The run() methods does not return any value.

Thread: Other methods


A thread may have methods other than the run() method. Here

is an example.

public boolean getOutcome(){

return (found); // Return the outcome of search }

Methods in a thread may be called during the execu_on of the

run() method and even azer the comple_on of the run()

method.

Thread: run() method


A run() method is like any other method except that it

does not have any parameters or return type.

A run() method may call any other method to complete its

task.

Thread: Crea_on


Create a thread object just as any other object.

The following examples create two thread objects named one

and two.

Search one=new Search (a, s, start, end, 1);

Search two=new Search (a, s, start, end, 2);

Thread: Start of execu_on


Execu_on of a thread must be started using the start() method

for that thread. Here are two examples for star_ng threads

one and two.

one.start(); // Starts the execu_on of thread object one

two.start(); // Starts the execu_on of thread object two

Thread: Wai_ng for comple_on


You may wait for a thread to complete execu_on using the join

() method as follows.

try{

one.join(); // Wait for thread one to complete

two.join(); // Wait for thread one to complete

catch(Excep_on e){}

The try-‐catch block is needed. More on this later!

Thread: Extrac_ng results


You may extract the outcome of a thread’s execu_on in a

variety of way. One way is to use an accessor method to do so.

Here are examples.

boolean f1=one.getOutcome(); // Get search outcome of thread one

boolean f2=two.getOutcome(); // Get search outcome of thread two

Thread: Typical lifecycle [Review]


Define class that extends Thread.

Create thread.

Start thread.

Wait for thread to terminate.

Get results from thread.

Use results from thread.

Example: Concurrent search


Problem 1


We are given a rather large array of strings. We wish to

write a program that will determine, and display, whether

or not a given string appears in the array.

Given that the array is large, we are required to write a

concurrent program that uses threads to solve the

problem faster than it would if done sequen_ally.

Understanding the problem


The problem is rather straighqorward!

Search algorithm


There are many search algorithms available. Given no

informa_on about how the array of strings is ordered, we will

use a simple linear search algorithm.

The given string will be compared with the first element of the

array, then the next and so on un_l a match is found or all

elements have been compared.

If a match is found, the algorithm returns true, otherwise it

returns false.

Concurrent search: Create threads


a=

0 1 2 3 4 5

q p

r

u

s

t

Given array

Create thread one Pass a, s and start and end indices to the constructor [start=0, end=2]

Given string to be searched: s

Create thread two Pass a, s and start and end indices to the constructor [start=3, end=5]

Concurrent search: Array par__oned


0 1 2

q p

r

3 4 5 u

s

t

Thread one searches in this part of the array

Thread two searches in this part of the array

Concurrent search: Next steps


•  Start the threads;

•  Wait for the threads to complete;

•  Extract the search outcome of each thread;

•  If any one of the threads found the string then the

search was successful otherwise the search failed.

Live demo


Challenge Problem


You are given an array of integers. The integers in the array vary from 0 (inclusive) to 500 (inclusive). You are also given 3 bins.

Write a concurrent program that distributes the integers in the

array into the 3 bins such that bin 1 gets all integers less than

170, bin 2 gets all integers greater than 170 but less than 240,

and bin 3 gets all integers greater than 240.

Sort the bins in ascending order and display.

Challenge Problem: Example


Given:

array={3, 43, 129, 32, 400, 452, 5}

Final contents of the three bins as displayed:

bin 1={3, 5, 32, 43} bin 2={129} bin 3={400, 452}

Week 12: November 7-‐11, 2011. Hope you enjoyed this week!

Ques_ons?

Contact your recita_on instructor. Make

full use of our office hours.


CS#180#Problem#Solving#and#ObjectOriented# …# name:# “Mango”# color:Yellow price:3.99#...

Documents

Transcript of CS#180#Problem#Solving#and#ObjectOriented# …# name:# “Mango”# color:Yellow price:3.99#...