Multithreading

To execute the java program in multitasking way, this concept is called as multi-threading.
      Multi-threading is used to overcome the idle time of CPU.

What is the procedure to create thread? And how it is execute?.

Inherit the java.lang.Thread class in user defined class. so our class becomes thread class. override the public void run() method thread class in our class. Create the object of our class. This is the new born stage of thread. Active this object using start() method of thread class. It will implicitly calls the overrides run() method.

Note : the program execution and time sharing to the threads are totally depends upon local operating system and the processor.

class A extends Thread
{
 public void run()
 {
 for(int i=1;i<=50;i++);
 System.out.println("i is "+i);
 }
}
class B extends Thread
{
 public void run()
 {
 for(int j=1;j<=50;j++);
 System.out.println("j is "+j);
 }
 
 public static void main(String args[])
 {
 A a1=new A();
 B b1=new B();
 
 a1.start();
 b1.start();
 
 for(int k=1;k<=50;k++)
 System.out.println("k is "+k)
 }
}

Another procedure to create and execute the Threads.       Implements the java.lang.Runable interface into user defined class, override it's only one method public void run() in our class. Still this is not the thread object, because our class is not extending the thread class.       So create the separate object of java.lang.Thread class and assign the user defined object of this thread object call the start() method using thread class object.       It will be implicitly calls the override run() method of respective object classes.

class AA extends object implements runnable
{
 public void run()
 {
 for(int i=1;i<=50;i++);
 System.out.println("i is "+i);
 }
}
class BB implements runnable
{
 public void run()
 {
 for(int j=1;j<=50;j++);
 System.out.println("j is "+j);
 }
 
 public static void main(String args[])
 {
 AA a1=new AA();
 BB b1=new BB();
 
 Thread f1=new Thread(a1);
 Thread f2=new Thread(b1);
 
 t1.start();
 t2.start();
 }
}

Thread controlling methods:

Methods which are used to manage the execution controlling of threads at running position.

1) sleep()

This method is used to interrupt the running thread for the given the interval in milliseconds. this interrupted thread will completing the time interval. This method throws interval. This method throws Interrupted Exception so we have to handle it at calling time.

class A extends Thread
{
 public void run()
 {
 for(int j=1;j<=50;j++);
 {
  try{
   if(j==15)
   thread.sleep(500);
  }
  catch(Exception e)
  {}
 System.out.println("j is "+j);
 }
 }
}
class B extends Thread
{
 public void run()
 {
 for(int i=1;i<=50;i++);
 System.out.println("i is "+i);
 }
 
 public static void main(String args[])
 {
 A a1=new A();
 B b1=new B();
 
 a1.start();
 b1.start();
 }
}

2) setPriority()

This method is used to set the execution of threads. It is just a request to local operating system. There are three type of priority:

1. Minimum priority => 1
2. Normal priority => 5
3. Maximum priority => 10

A a1=new A();
B b1=new B();
C c1=new C();

a1.setPriority(10);
b1.setPriority(7);
c1.setPriority(5);

a1.start();
b1.start();
c1.start();

3) join()

This method is used to join or connect or connect one thread to other, so that the other thread will complete it's execution and normal goes into dead stage.

What is the procedure to kill any thread ?.

Use stop() method to kill the thread abnormally, but it is deprecated from java library. and it's replacement method join().

Write a program to join one thread to another using join() method.

class D extends Thread
{
 public D extends Thread
 {
  for(int i=1;i<=5000;i++)
  System.out.println("i is "+i);
 }
}
class E extends Thread
{
 D d1;
 E(D d1) //pass the reference from
 {
  this.d1=d1;
 }
 public void run()
 {
 for(int j=1;j<=50;j++)
  {
   try{
    if(j==15)
    d1.join();
   }
   catch(Exception e);
   {}
   
   System.out.println("j is "+j);
  }
 }
 
 public static void main(String args[])
 {
  D d1=new D();
  E e1=new E()d1; //pass reference to constructor
  
  d1.start();
  e1.start();
 }
}

Synchronization :

To execute the thread based program in process way, this concept is called as synchronization.

Keyword "synchronized" is used to define such methods.

class Test
{
 Synchronized public void fun1(String args[])
 {
  System.out.println(" [ Hello ");
  try
  {
   Thread.sleep(1000);
  }
  catch(Exception e1)
  {}
  System.out.println(" [ "+msg);
  try
  {
   Thread.sleep(1000);
  }
  catch(Exception e)
  {}
  System.out.println(" ] world ] ");
 }
}
class AB extends Thread
{
 Test t1;
 AB(Test t1)
 {
  this.t1=t1;
 }
 
 public void run()
 {
  t1.fun1("java");
 }
}
class BC extends Thread
{
 Test t1;
 BC(Test t1)
 {
  this.t1=t1;
 }
 
 public void run()
 {
  t1.fun1("C++");
 }
 
 public static void main(String args[])
 {
  Test t1=new Test();
  
  AB a1=new AB(t1);
  BC b1=new BC(t1);
  
  a1.start();
  b1.start();
 }
}