Java Thread Exceptions

What is thread exception

• When thread method is called which is throwing an exception the appropriate exception handler must be supplied which catch the exception thrown by thread.
• Mostly call to sleep () method is enclosed within a try block and followed by catch block. This is because the sleep() method threads an exception, which must be caught. If exception thread is not catched, program will not compile.
• Java run system will throw IllegalThreadStateException whenever attempt is made to invoke a method that a thread cannot handle in given state.
• Example - a sleeping thread cannot deal with the resume () method because a sleeping thread cannot receive any instructions. Even for suspend() method when it is used on a block or NotRunnable thread.

Exceptions generated by Thread

Most commonly exceptions fetched by a thread are

1. ThreadDeath
2. InterruptedException
3. IllegalArgumentException
4. Exception

1. ThreadDeath exception example

System.out.println("Trying to kill current thread");
try 
{
    Thread.currentThread().stop();
} 
catch (final ThreadDeath ex) 
{
    System.out.println("I'm dead");
    throw ex;
}

2. Interrupted exception example

 try 
{
    for (int i = 0; i < 5; i++) 
    {
        System.out.println(Thread.currentThread().getName());
        Thread.sleep(1000);
        Thread.currentThread().interrupt();
    }

} 
catch (InterruptedException e) 
{
    e.printStackTrace();
}

3. IllegalArgumentException example

void setPercentage(int pct) {
    if( pct < 0 || pct > 100) {
         throw new IllegalArgumentException("bad percent");
     }
}

4. Exception example

System.out.println("Trying to kill current thread");
try 
{
    Thread.currentThread().stop();
} 
catch (Exception ex) 
{
    System.out.println("I'm dead");
    throw ex;
}

Thread Priority

Priority decides the execution time of thread. It means at what time the thread is to be executed.

Thread is assigned a priority, which affects the order in which it is scheduled for execution or runnning.

What are the Thread priorities?

Thread priorities are integers that specify the relative priority. They are between 1 to 10

Priorities :

1. MIN_PRIORITY = 1
2. NORM_PRIORITY = 6
3. MAX_PRIORITY = 10

Note : By default the thread have NORM_PRIORITY = 6

How to set priority to thread

The thread priority can be assigned by using following method.

ThreadName.setPriority (int Value)

Example

class A extends Thread
{
    public void run()
    {
	System.out.println("Thread A started");
	for(int i=1;i<=5;i++)
	   System.out.println("A : "+i);
			
	System.out.println("Thread A exited");
    }
}
class B extends Thread
{
    public void run()
    {
	System.out.println("Thread B started");
		
	for(int i=1;i<i++)
	   System.out.println("B : "+i);
		
	System.out.println("Thread B exited");
    }
}
class C extends Thread
{
    public void run()
    {
	System.out.println("Thread C started");
	for(int i=1;i<=5;i++)
	    System.out.println("C : "+i);
			
	System.out.println("Thread C exited");
    }
}
public class Test {
	public static void main(String[] args) 
        {
	    A a1 = new A();
	    B b1 = new B();
	    C c1 = new C();
		
	    a1.setPriority(Thread.MAX_PRIORITY);
	    b1.setPriority(Thread.MIN_PRIORITY);
	    c1.setPriority(7);
		
	    a1.start();
	    b1.start();
	    c1.start();
	}
}

Output

How to get priority of thread?

To get the current priority of thread, Following method is used.

int getPriority ()

This method will return the integer value as a priority

Example - From above example it will return the priority of Thread A as 10

a1.getPriority();