Thread Methods in Java
Thread in Java
In this lesson, we will learn about the most commonly used methods of Thread class and how to use them to control threads in java.
Thread Methods in Java?
There are several methods available in the Thread class, but here we will discuss the most commonly used methods of the Thread class and their uses in Java.
run() and start() Method
In the run() method, we write the codes we want to execute in a thread, and the start() method is used to execute the code written in the run() method on a child thread.
Example
class ThreadA extends Thread
{
public void run()
{
int i,j,fc;
for(i=1; i<=10; i++)
{
fc=0;
for(j=1; j<=i; j++)
{
if(i%j==0)
{
fc++;
}
}
if(fc==2)
{
System.out.println("Prime Number = "+i);
}
}
}
}
public class Example
{
public static void main(String args[])
{
ThreadA a = new ThreadA();
// execute the thread
a.start();
}
}Output
Prime Number = 2 Prime Number = 3 Prime Number = 5 Prime Number = 7
sleep() Method
The sleep() method is used to pause the execution of a running thread for specified milliseconds (1000 milliseconds = 1 second). The thread starts running when the specified time for the sleep() method is over.
This method is used in a try-catch block because it raises the InterruptedException exception.
Example
class ThreadA extends Thread
{
public void run()
{
int i;
for(i=1; i<=5; i++)
{
System.out.println(i);
try
{
// pause the thread for 2 seconds
Thread.sleep(2000);
}
catch(InterruptedException e) {}
}
}
}
public class Example
{
public static void main(String args[])
{
ThreadA a = new ThreadA();
// execute the thread
a.start();
}
}Output
1 2 3 4 5
In the above program, we pause the child thread ThreadA for 2 seconds using the sleep() method, so each number on the output screen will appear after 2 seconds.
join() Method
The currently running thread is put into a wait state by the join() method until the thread on which the join() method was called has finished running.
This method is used in a try-catch block because it raises the InterruptedException exception.
Example
class ThreadA extends Thread
{
public void run()
{
int i;
for(i=1; i<=5; i++)
{
System.out.println(i);
try
{
Thread.sleep(1000);
}
catch(InterruptedException e) {}
}
System.out.println("Exit from ThreadA");
}
}
class ThreadB extends Thread
{
public void run()
{
int i;
for(i=10; i<=15; i++)
{
System.out.println(i);
try
{
Thread.sleep(3000);
}
catch(InterruptedException e) {}
}
System.out.println("Exit from ThreadB");
}
}
public class Example
{
public static void main(String args[])
{
ThreadA a = new ThreadA();
ThreadB b = new ThreadB();
// execute the thread
a.start();
b.start();
try
{
a.join();
}
catch(InterruptedException e) {}
System.out.println("End of main thread");
}
}Output
1 10 2 3 11 4 5 Exit from ThreadA End of main thread 12 13 14 15 Exit from ThreadB
In the above program, we have invoked the join() method on the object of class ThreadA. The join() method puts the main thread into a wait state until the ThreadA has completed its execution.
isAlive() Method
The isAlive() method is used to check whether a thread is alive. This method returns true if the thread is alive and returns false if the thread is not alive.
Example
class ThreadA extends Thread
{
public void run()
{
int i;
System.out.println("Even numbers between 1 to 10");
for(i=1; i<=10; i++)
{
if(i%2==0)
{
System.out.println(i);
try
{
// pause the thread for 2 seconds
Thread.sleep(2000);
}
catch(InterruptedException e) {}
}
}
}
}
public class Example
{
public static void main(String args[])
{
ThreadA a = new ThreadA();
// execute the thread
a.start();
System.out.println("Thread is alive: " + a.isAlive());
try
{
a.join();
}
catch(InterruptedException e) {}
System.out.println("Thread is alive: " + a.isAlive());
}
}Output
Thread is alive: true Even numbers between 1 to 10 2 4 6 8 10 Thread is alive: false
getId() Method
The getId() method is used to get the ID number of a thread. The thread ID is a positive number generated when a thread is created. The thread ID is unique and remains unchanged during the lifetime of a thread. When a thread is terminated, the thread ID may be reused.
Example
class ThreadA extends Thread
{
public void run()
{
System.out.println("Hello I am child thread");
}
}
public class Example
{
public static void main(String args[])
{
ThreadA a = new ThreadA();
// execute the thread
a.start();
System.out.println("Thread ID: " + a.getId());
}
}Output
Thread ID: 8 Hello I am child thread
setName() and getName() Method
The setName() method is used to set a new name of a thread. The getName() method is used to get the name of a thread.
Example
class ThreadA extends Thread
{
public void run()
{
System.out.println("Hello I am child thread");
}
}
public class Example
{
public static void main(String args[])
{
ThreadA a = new ThreadA();
System.out.println("Thread Name: " + a.getName());
a.setName("delta56");
a.start();
System.out.println("Thread Name: " + a.getName());
}
}Output
Thread Name: Thread-0 Thread Name: delta56 Hello I am child thread
getState() Method
The getState() method is used to get the state of a thread. The state means in which form the thread is working in the processor.
Example
class ThreadA extends Thread
{
public void run()
{
System.out.println("Hello I am child thread");
}
}
public class Example
{
public static void main(String args[])
{
ThreadA a = new ThreadA();
System.out.println("Thread State: " + a.getState());
a.start();
System.out.println("Thread State: " + a.getState());
try
{
a.join();
}
catch(InterruptedException e) {}
System.out.println("Thread State: " + a.getState());
}
}Output
Thread State: NEW Thread State: RUNNABLE Hello I am child thread Thread State: TERMINATED
setPriority() Method
The setPriority() method is used to set the running priority of a thread in the processor. There are three types of thread priority, and they are:
- MIN_PRIORITY means minimum priority whose constant value is 1.
- NORM_PRIORITY means normal priority whose constant value is 5.
- MAX_PRIORITY means maximum priority whose constant value is 10.
Example
class ThreadA extends Thread
{
public void run()
{
int i,j,fc,pc=0;
for(i=1; i<=90000; i++)
{
fc=0;
for(j=1; j<=i; j++)
{
if(i%j==0)
{
fc++;
}
}
if(fc==2)
{
pc++;
}
}
System.out.println("ThreadA -> Total Prime Number = "+pc);
}
}
class ThreadB extends Thread
{
public void run()
{
int i,j,fc,pc=0;
for(i=1; i<=90000; i++)
{
fc=0;
for(j=1; j<=i; j++)
{
if(i%j==0)
{
fc++;
}
}
if(fc==2)
{
pc++;
}
}
System.out.println("ThreadB -> Total Prime Number = "+pc);
}
}
class ThreadC extends Thread
{
public void run()
{
int i,j,fc,pc=0;
for(i=1; i<=90000; i++)
{
fc=0;
for(j=1; j<=i; j++)
{
if(i%j==0)
{
fc++;
}
}
if(fc==2)
{
pc++;
}
}
System.out.println("ThreadC -> Total Prime Number = "+pc);
}
}
public class Example
{
public static void main(String args[])
{
ThreadA a=new ThreadA();
ThreadB b=new ThreadB();
ThreadC c=new ThreadC();
a.setPriority(1);
b.setPriority(5);
c.setPriority(10);
a.start();
b.start();
c.start();
}
}Output
ThreadC -> Total Prime Number = 8713 ThreadB -> Total Prime Number = 8713 ThreadA -> Total Prime Number = 8713
In the above program, we created three threads that count the number of prime numbers between 1 and 90000. We set the priority of ThreadA's object to 1 (MIN_PRIORITY), ThreadB's object to 5 (NORM_PRIORITY), and ThreadC's object to 10 (MAX_PRIORITY).
Because the priority of the ThreadC is set to 10, which is the highest priority, it will get more time in the processor for its code execution. The ThreadB will get a normal amount of time in the processor for its code execution, and ThreadA will get a time below the normal time for its code execution.
If we run the above program several times, we can see that the ThreadC completes its execution first compared to the other two threads because it is getting more time in the processor for its code execution than the other two threads.
getPriority() Method
The getPriority() method is used to get the priority of a thread.
Example
class ThreadA extends Thread
{
public void run()
{
System.out.println("I am ThreadA with MAX_PRIORITY");
}
}
class ThreadB extends Thread
{
public void run()
{
System.out.println("I am ThreadB with NORM_PRIORITY");
}
}
public class Example
{
public static void main(String args[])
{
ThreadA a=new ThreadA();
ThreadB b=new ThreadB();
a.setPriority(10);
System.out.println("ThreadA priority: " + a.getPriority());
System.out.println("ThreadB priority: " + b.getPriority());
a.start();
b.start();
}
}Output
ThreadA priority: 10 ThreadB priority: 5 I am ThreadA with MAX_PRIORITY I am ThreadB with NORM_PRIORITY
Note: By default, the priority of a thread is 5 (NORM_PRIORITY) unless we set a new priority for the thread.
