Multithreading

1. Multithreading • A thread is the flow of execution, from beginning to end, of a task in a program. • With Java, you can launch multiple threads from a program concurrently. • These threads can be executed simultaneously in multiprocessor systems. • In single processor system, multiple threads share CPU time

2. Runnable interface • When your program executes as an application, Java interpreter starts a thread for the main method. • When your program executes as an applet, the web browser starts a thread to run the applet. • You can create additional threads to run concurrent task in the program. • Each new thread is an object of a class that implements the Runnable interface or extends a class that implements the Runnable interface. • You can create threads either by extending the Thread class or by implementing the Runnable interface. • Both Thread and Runnable are defined in the java.lang

3. Creating Threads by Extending Thread class • Thread class contains • Constructors • Many useful method controlling the thread • To create and run a thread • Define a class that extends Thread • Must override the run() method, which tells the system how the thread will be executed when it runs • Create an object running on the thread

4. Figure // custom thread class public class myThread extends Thread { // constructor public myThread() { ….. } // override the run method public void run() { // tell system how to run … } … }// end of class myThread // client class public class client { ….. // some method public void someMethod() { // create a thread myThread th = new myThread(); // start a thread; th.start(); … } … }// end of class myThread

5. Example • Problem: write a program that creates and runs three threads: • The first thread prints the letter a one hundred times • The second thread prints the letter b one hundred times • The third thread prints the integers 1 through 100. • Solution: • The program has three independent threads. • To run them concurrently, it needs to create a runnable object for each thread • The first two thread have similarity, we can define in one thread class and create two different thread for letter a and b.

6. Program code // TestThread.java public class TestThread{ public static void main(String [] args) { // create threads PrintChar printA = new PrintChar(‘a’,100); PrintChar printB = new PrintChar(‘b’, 100); PrintNum print100 = new PrintNum (100); // start threads printA.start(); printB.start(); print100.start(); } // end of main }// end of class TestThread

7. Program code - continued class PrintChar extends Thread{ private char charToPrint; private int times; // construcotr public PrintChar(char x, int n){ charToPrint = x; times = n; } // override run() method public void run() { for ( int I = 0; I < times; I++) System.out.print (charToPrint); }

8. Program code - continued // the thread class for printing number from 1-n class PrintNum extends Thread { private int lastNum; // constructor public PrintNum( int n) { lastNum = n; } // override run() method public void run(){ for ( int I = 0; I < ladtNum; I++) System.out.print( I + “ “); } // end of run } // end of class

9. Implementing Runnable Interface • Java have no multiple inheritance • Java provides Runnable interface as alternative to the Thread class • Runnable interface just contain the run() method • You need to implement this method to tell system how your thread is going to run

10. // client class public class client { ….. // some method public void someMethod() { // create an instance of myThread myThread myth = new myThread(…); // create a thread Thread th = new Thread(myth); // start a thread; th.start(); … } … }// end of class myThread // custom thread class public class myThread implements Runnable { // constructor public myThread() { ….. } // implement the run method public void run() { // tell system how to run … } … }// end of class myThread

11. Program Code public class testRunnable{ // create threads Thread printA = new Thread(new PrintChar(‘a’,100)); Thread printB = new Thread(new PrintChar(‘b’,100)); Thread print100 = new Thread (new PrintNum(100)); public static void main(String []args){ new TestRunnable(); }

12. Program code - continued public TestRunnable(){ printA.start(); printB.start(); print100.start(); } // thread class for printing letter a or b class PrintChar implements Runnable{ private char charToPrint; private int times; public PrintChar(char c, int t){ charToPrint = c; times = t; }

13. Program code - continued // override the run method public void run(){ for ( int i = 0; i <times; i++) System.out.print(charToPrint); } }// end of class

14. Program code -continued // class for printing number from 1 to n Class PrintNum implements Runnable{ private int lastNum; public PrintNum(int n){ lastNum = n; } // override run() Public void run(){ for ( int I = 0; I < lastNum; i++){ System.out.print(“ “ + i); } } }