Academic Tutorials



English | French | Portugese | German | Italian
Home Advertise Payments Recommended Websites Interview Questions FAQs
News Source Codes E-Books Downloads Jobs Web Hosting
Chats

Java Tutorial
Java Introduction
Object Oriented Programming Concepts
Anatomy of a Java Application
Syntax and Semantics of Java
Java Objects, Classes, and Interfaces
The String and StringBuffer Classes in Java
Setting Program Attributes in Java
Using System Resources in Java
Threads of Control in Java
Errors and Exceptions in Java
Java Input and Output Streams
Overview of Java Applet
Creating an Applet User Interface in Java
Communicating with Other Programs in Java
Overview of the Java UI
Using GUI Building Blocks in Java
Laying Out Components within a Container
Working with Graphics in Java
How Java Differs from C and C++
Java Summary

HTML Tutorials
HTML Tutorial
XHTML Tutorial
CSS Tutorial
TCP/IP Tutorial
CSS 1.0
CSS 2.0
HLML
XML Tutorials
XML Tutorial
XSL Tutorial
XSLT Tutorial
DTD Tutorial
Schema Tutorial
XForms Tutorial
XSL-FO Tutorial
XML DOM Tutorial
XLink Tutorial
XQuery Tutorial
XPath Tutorial
XPointer Tutorial
RDF Tutorial
SOAP Tutorial
WSDL Tutorial
RSS Tutorial
WAP Tutorial
Web Services Tutorial
Browser Scripting
JavaScript Tutorial
VBScript Tutorial
DHTML Tutorial
HTML DOM Tutorial
WMLScript Tutorial
E4X Tutorial
Server Scripting
ASP Tutorial
PERL Tutorial
SQL Tutorial
ADO Tutorial
CVS
Python
Apple Script
PL/SQL Tutorial
SQL Server
PHP
.NET (dotnet)
Microsoft.Net
ASP.Net
.Net Mobile
C# : C Sharp
ADO.NET
VB.NET
VC++
Multimedia
SVG Tutorial
Flash Tutorial
Media Tutorial
SMIL Tutorial
Photoshop Tutorial
Gimp Tutorial
Matlab
Gnuplot Programming
GIF Animation Tutorial
Scientific Visualization Tutorial
Graphics
Web Building
Web Browsers
Web Hosting
W3C Tutorial
Web Building
Web Quality
Web Semantic
Web Careers
Weblogic Tutorial
SEO
Web Site Hosting
Domain Name
Java Tutorials
Java Tutorial
JSP Tutorial
Servlets Tutorial
Struts Tutorial
EJB Tutorial
JMS Tutorial
JMX Tutorial
Eclipse
J2ME
JBOSS
Programming Langauges
C Tutorial
C++ Tutorial
Visual Basic Tutorial
Data Structures Using C
Cobol
Assembly Language
Mainframe
Forth Programming
Lisp Programming
Pascal
Delphi
Fortran
OOPs
Data Warehousing
CGI Programming
Emacs Tutorial
Gnome
ILU
Soft Skills
Communication Skills
Time Management
Project Management
Team Work
Leadership Skills
Corporate Communication
Negotiation Skills
Database Tutorials
Oracle
MySQL
Operating System
BSD
Symbian
Unix
Internet
IP-Masquerading
IPC
MIDI
Software Testing
Testing
Firewalls
SAP Module
ERP
ABAP
Business Warehousing
SAP Basis
Material Management
Sales & Distribution
Human Resource
Netweaver
Customer Relationship Management
Production and Planning
Networking Programming
Corba Tutorial
Networking Tutorial
Microsoft Office
Microsoft Word
Microsoft Outlook
Microsoft PowerPoint
Microsoft Publisher
Microsoft Excel
Microsoft Front Page
Microsoft InfoPath
Microsoft Access
Accounting
Financial Accounting
Managerial Accounting
Network Sites


Threads of Control in Java


Previoushome Next





Definition: A thread is nothing but a single sequential flow of control within the program.


A D V E R T I S E M E N T



What is Thread?

Programmers are familiar with writing sequential programs. The program that displays "Hello World!", or program which sorts a list of names, or computes the list of prime numbers, are sequential all programs: each has beginning, end, sequence, and at any given time during runtime of program there is single point of execution.

A thread is similar to a sequential program, a single thread do also has beginning, end, sequence, and at any given time during runtime of thread there will be a single point of execution. But the thread itself is not a program it cannot run by itself but runs within the program.




Simple Thread example

The following example is a simple Java application that will create and start two independent threads.

class TwoThreadsTest
{
public static void main (String args[])
{
new SimpleThread("Japan").start();
new SimpleThread("India").start();
}
}

class SimpleThread extends Thread
{
public SimpleThread(String str)
{
super(str);
}
public void run()
{
for (int i = 0; i < 10; i++)
{
System.out.println(i + " " + getName());
try
{
sleep((int)(Math.random() * 1000));
} catch (InterruptedException e)
{}
}
System.out.println("DONE! " + getName());
}
}

The first method in SimpleThread class is a constructor which takes only String as its argument. This constructor is implemented by calling the superclass constructor and is interesting because it sets Thread's name which is been used later in the program.

The next method in this class is run() method. run() method is the heart of any Thread, this is where the action of the Thread takes place. The run() method in the SimpleThread class contains a for loop which iterates ten times. In each of the iteration it displays the iteration number and name of the Thread and then sleeps for random interval of time between 0 and 1 second. After finishing the loop, the run() method prints "DONE!" along with the name of thread.




Attributes of a Thread

All the action takes place in the thread's body, in the thread's run() method. We can provide the body to Thread in one of the two ways: first by subclassing a Thread class and overriding the run() method of thread, secondly by creating a Thread with Runnable object as its target.




Body of a Thread

Java threads are implemented by using Thread class which is the part of java.lang package. A Thread class implements the system independent definition of Java threads. But, actual implementation of the concurrent operation is provided by the system-specific implementation. For most of the programming needs, underlying implementation doesn't matter; we can ignore the underlying implementation and program the thread API and other documentation provided with the Java system.




States of a Thread

Throughout the life, Java thread will be in one among several states. The state of a thread indicates what the Thread is doing currently and what it can do at that time of its life: whether it is running? is sleeping? or is dead? These states are illustrated below.




New Thread
The statement below creates a new thread but it will not start it thereby leaving the thread in a state labeled "New Thread".

Thread myThread = new MyThreadClass();

When the thread is in "New Thread" state, merely it is an empty Thread object. No system resources are allocated for it yet. Thus when the thread is in this state, we can only start or stop the thread; when a thread is in this state calling any of the other method besides start() or stop() will not make any sense and causes an IllegalThreadStateException.

Runnable
The start() method creates all the necessary system resources to run a thread, It schedules the thread to run, and calls thread's run() method.

Thread myThread = new MyThreadClass();
myThread.start();

At this point the thread is in "Runnable" state. This state is called "Runnable" state rather than "Running" state because the thread may not be running actually when it is in this state. Many computers do have a single processor making it impossible to run all the "Runnable" threads at the same time. Therefore the Java runtime system should implement the scheduling scheme which shares the processor between all the "Runnable" threads. For most of the purposes however, we can think of "Runnable" state as simply "Running". When a thread is running, it is "Runnable" and is the current thread. The instructions in the run() method are executing sequentially.

Not Runnable
A thread enters into "Not Runnable" state when one of following events occur:

  • When a suspend() method is called
  • When a sleep() method is called
  • When the thread uses its wait() method to wait for a condition variable
  • When the thread is blocking on I/O.

Thread myThread = new MyThreadClass();
myThread.start();
try
{
myThread.sleep(10000);
} catch (InterruptedException e)
{
}

The bold line in the above example puts myThread to sleep for 10 seconds. During these 10 seconds, even if the processor becomes available myThread will not run. After 10 seconds are over, myThread becomes "Runnable" again and if the processor is available it would run.

Following statements indicates the escape route for every entrance into "Not Runnable" state.

  • If the thread is put to sleep, then the specified time should elapse.
  • If the thread is suspended, then someone must call the resume() method.
  • If the thread is waiting on condition variable, whatever object owns the variable should relinquish this by calling either notify() or notifyAll() method.
  • If the thread is been blocked on I/O, then the specified I/O command should get complete.

Dead
A thread can die in two different ways: either by a natural cause, or being killed (stopped). A thread is said to die naturally when the run() method exits normally. Cosider for example, the while loop in the run method is a finite loop, it will iterate 100 times and then stops executing.

public void run()
{
int i = 0;
while (i < 100)
{
i++;
System.out.println("i = " + i);
}
}

We can also kill a thread any time simply by calling the stop() method. This is as shown in the code below:

public void run()
{
Thread myThread = new MyThreadClass();
myThread.start();
try
{
Thread.currentThread().sleep(10000);
} catch (InterruptedException e)
{
}
myThread.stop();
}

The run method here creates and starts myThread then it puts the current thread to sleep for some 10 seconds. When current thread wakes up, the bold line in the code segment will kill myThread.

The stop() method will throw a ThreadDeath object to kill the thread. When the thread is killed in this manner it dies asynchronously. Thread will die when it actually receives a ThreadDeath exception.

IllegalThreadStateException
runtime system throws an IllegalThreadStateException when we call a method on a thread and the thread's state will not allow for that method call. For example, IllegalThreadStateException is thrown when we call a suspend() method on a thread which is not "Runnable".

As per in the examples of threads studied so far in this chapter, when we call a thread method which can throw an exception, you should either catch and handle the exception, or should declare that, the calling method throws uncaught exception.

public void run()
{
Thread myThread = new MyThreadClass();
myThread.start();
try
{
Thread.currentThread().sleep(10000);
} catch (InterruptedException e)
{
}
myThread.stop();
}

isAlive() Method

If the method isAlive() returns true then thread is started and not stopped. Thus, if isAlive() method returns false we know that the thread is either "New Thread" or "Dead" one . If isAlive() method returns true, you then the thread is either "Runnable" or "Not Runnable".




Thread Priority

When a Java thread is created, it inherits the priority from the thread that created it. We can also modify the thread's priority any time after its creation using the method setPriority(). Threads priorities range from MIN_PRIORITY to MAX_PRIORITY (these are the constants defined in class Thread). At any given instant of time, when multiple threads are ready to execute, the runtime system chooses "Runnable" thread having the highest priority for execution. Only when this thread stops, yields, or becomes "Not Runnable" for some sort of reason, the lower priority thread start executing. If there are two threads having same priority waiting for CPU, the scheduler will choose them in a round-robin fashion.




Daemon Threads

Any Java thread can be daemon thread. Daemon threads are service providers for those threads or objects running in same process as the daemon thread is running. For example, HotJava browser has a daemon thread, called Background Image Reader, which reads images from the file system or network for any of the object or thread which needs an image.



Be the first one to comment on this page.




  Java Tutorial eBooks
More Links » »
 
 Java Tutorial FAQs
More Links » »
 
 Java Tutorial Interview Questions
More Links » »
 
 Java Tutorial Articles
More Links » »
 
 Java Tutorial News
More Links » »
 
 Java Tutorial Jobs
More Links » »

Share And Enjoy:These icons link to social bookmarking sites where readers can share and discover new web pages.
  • blinkbits
  • BlinkList
  • blogmarks
  • co.mments
  • connotea
  • del.icio.us
  • De.lirio.us
  • digg
  • Fark
  • feedmelinks
  • Furl
  • LinkaGoGo
  • Ma.gnolia
  • NewsVine
  • Netvouz
  • RawSugar
  • Reddit
  • scuttle
  • Shadows
  • Simpy
  • Smarking
  • Spurl
  • TailRank
  • Wists
  • YahooMyWeb

Previoushome Next

Keywords: multiple threads, java threads lock, scott oaks, henry wong

HTML Quizzes
HTML Quiz
XHTML Quiz
CSS Quiz
TCP/IP Quiz
CSS 1.0 Quiz
CSS 2.0 Quiz
HLML Quiz
XML Quizzes
XML Quiz
XSL Quiz
XSLT Quiz
DTD Quiz
Schema Quiz
XForms Quiz
XSL-FO Quiz
XML DOM Quiz
XLink Quiz
XQuery Quiz
XPath Quiz
XPointer Quiz
RDF Quiz
SOAP Quiz
WSDL Quiz
RSS Quiz
WAP Quiz
Web Services Quiz
Browser Scripting Quizzes
JavaScript Quiz
VBScript Quiz
DHTML Quiz
HTML DOM Quiz
WMLScript Quiz
E4X Quiz
Server Scripting Quizzes
ASP Quiz
PERL Quiz
SQL Quiz
ADO Quiz
CVS Quiz
Python Quiz
Apple Script Quiz
PL/SQL Quiz
SQL Server Quiz
PHP Quiz
.NET (dotnet) Quizzes
Microsoft.Net Quiz
ASP.Net Quiz
.Net Mobile Quiz
C# : C Sharp Quiz
ADO.NET Quiz
VB.NET Quiz
VC++ Quiz
Multimedia Quizzes
SVG Quiz
Flash Quiz
Media Quiz
SMIL Quiz
Photoshop Quiz
Gimp Quiz
Matlab Quiz
Gnuplot Programming Quiz
GIF Animation Quiz
Scientific Visualization Quiz
Graphics Quiz
Web Building Quizzes
Web Browsers Quiz
Web Hosting Quiz
W3C Quiz
Web Building Quiz
Web Quality Quiz
Web Semantic Quiz
Web Careers Quiz
Weblogic Quiz
SEO Quiz
Web Site Hosting Quiz
Domain Name Quiz
Java Quizzes
Java Quiz
JSP Quiz
Servlets Quiz
Struts Quiz
EJB Quiz
JMS Quiz
JMX Quiz
Eclipse Quiz
J2ME Quiz
JBOSS Quiz
Programming Langauges Quizzes
C Quiz
C++ Quiz
Visual Basic Quiz
Data Structures Using C Quiz
Cobol Quiz
Assembly Language Quiz
Mainframe Quiz
Forth Programming Quiz
Lisp Programming Quiz
Pascal Quiz
Delphi Quiz
Fortran Quiz
OOPs Quiz
Data Warehousing Quiz
CGI Programming Quiz
Emacs Quiz
Gnome Quiz
ILU Quiz
Soft Skills Quizzes
Communication Skills Quiz
Time Management Quiz
Project Management Quiz
Team Work Quiz
Leadership Skills Quiz
Corporate Communication Quiz
Negotiation Skills Quiz
Database Quizzes
Oracle Quiz
MySQL Quiz
Operating System Quizzes
BSD Quiz
Symbian Quiz
Unix Quiz
Internet Quiz
IP-Masquerading Quiz
IPC Quiz
MIDI Quiz
Software Testing Quizzes
Testing Quiz
Firewalls Quiz
SAP Module Quizzes
ERP Quiz
ABAP Quiz
Business Warehousing Quiz
SAP Basis Quiz
Material Management Quiz
Sales & Distribution Quiz
Human Resource Quiz
Netweaver Quiz
Customer Relationship Management Quiz
Production and Planning Quiz
Networking Programming Quizzes
Corba Quiz
Networking Quiz
Microsoft Office Quizzes
Microsoft Word Quiz
Microsoft Outlook Quiz
Microsoft PowerPoint Quiz
Microsoft Publisher Quiz
Microsoft Excel Quiz
Microsoft Front Page Quiz
Microsoft InfoPath Quiz
Microsoft Access Quiz
Accounting Quizzes
Financial Accounting Quiz
Managerial Accounting Quiz
Testimonials | Contact Us | Link to Us | Site Map
Copyright 2008. Academic Tutorials.com. All rights reserved Privacy Policies | About Us
Our Portals : Academic Tutorials | Best eBooksworld | Beyond Stats | City Details | Interview Questions | Discussions World | Excellent Mobiles | Free Bangalore | Give Me The Code | Gog Logo | Indian Free Ads | Jobs Assist | New Interview Questions | One Stop FAQs | One Stop GATE | One Stop GRE | One Stop IAS | One Stop MBA | One Stop SAP | One Stop Testing | Webhosting in India | Dedicated Server in India | Sirf Dosti | Source Codes World | Tasty Food | Tech Archive | Testing Interview Questions | Tests World | The Galz | Top Masala | Vyom | Vyom eBooks | Vyom International | Vyom Links | Vyoms | Vyom World
Copyright 2003-2017 Vyom Technosoft Pvt. Ltd., All Rights Reserved.