Java Thread Class

Last Updated : 10 Jan, 2025

Thread is a line of execution within a program. Each program can have multiple associated threads. Each thread has a priority which is used by the thread scheduler to determine which thread must run first. Java provides a thread class that has various method calls to manage the behavior of threads by providing constructors and methods to perform operations on threads.

A Thread is a program that starts with a method() frequently used in this class only known as the start() method. This method looks out for the run() method which is also a method of this class and begins executing the body of the run() method. Here, keep an eye on the sleep() method which will be discussed later below.

Note: Every class that is used as a thread must implement Runnable interface and override its run method.

Syntax

public class Thread extends Object implements Runnable

Constructors of Thread Class

Constructor	Action Performed
Thread()	Allocates a new Thread object.
Thread(Runnable target)	Allocates a new Thread object.
Thread(Runnable target, String name)	Allocates a new Thread object.
Thread(String name)	Allocates a new Thread object.
Thread(ThreadGroup group, Runnable target)	Allocates a new Thread object.
Thread(ThreadGroup group, Runnable target, String name)	Allocates a new Thread object so that it has targeted as its run object, has the specified name as its name, and belongs to the thread group referred to by a group.
Thread(ThreadGroup group, Runnable target, String name, long stackSize)	Allocates a new Thread object so that it has targeted as its run object, has the specified name as its name, and belongs to the thread group referred to by group, and has the specified stack size.
Thread(ThreadGroup group, String name)	Allocates a new Thread object.

Example: Java program to demonstrate usage of Thread class

Java

// Java Program to demonstrate // usage of Thread class  class MyThread extends Thread  {   	// Overriding the run method   	@Override     public void run()      {         for (int i = 0; i < 5; i++)          {             System.out.println(Thread.currentThread().getName()                                + " - Count : " + i);                        	try {               	// Sleep for 500 milliseconds                 Thread.sleep(500);              }            	catch (InterruptedException e) {                 System.out.println("Thread interrupted");             }         }     } }  // Main Class public class Geeks  {     public static void main(String[] args)      {         MyThread thread1 = new MyThread();         MyThread thread2 = new MyThread();          thread1.setName("Thread 1");         thread2.setName("Thread 2");        	// Start thread 1         thread1.start();               	// Start thread 2         thread2.start();      } }

Output:

Thread 1 - Count : 0
Thread 2 - Count : 0
Thread 1 - Count : 1
Thread 2 - Count : 1
Thread 1 - Count : 2
Thread 2 - Count : 2
Thread 1 - Count : 3
Thread 2 - Count : 3
Thread 2 - Count : 4
Thread 1 - Count : 4

Note: Execution of the thread is not according to the sequence, it can be executed in any sequence Thread 1 then Thread 2 , or Thread 2 then Thread 1.

Methods of Thread Class

Methods	Action Performed
activeCount()	Returns an estimate of the number of active threads in the current thread's thread group and its subgroups
checkAccess()	Determines if the currently running thread has permission to modify this thread
clone()	Throws CloneNotSupportedException as a Thread can not be meaningfully cloned
currentThread()	Returns a reference to the currently executing thread object
dumpStack()	Prints a stack trace of the current thread to the standard error stream
enumerate(Thread[] tarray)	Copies into the specified array every active thread in the current thread's thread group and its subgroups
getAllStackTraces()	Returns a map of stack traces for all live threads
getContextClassLoader()	Returns the context ClassLoader for this Thread
getDefaultUncaughtExceptionHandler()	Returns the default handler invoked when a thread abruptly terminates due to an uncaught exception
getId()	Returns the identifier of this Thread
getName()	Returns this thread's name
getPriority()	Returns this thread's priority
getStackTrace()	Returns an array of stack trace elements representing the stack dump of this thread
getState()	Returns the state of this thread
getThreadGroup()	Returns the thread group to which this thread belongs
getUncaughtExceptionHandler()	Returns the handler invoked when this thread abruptly terminates due to an uncaught exception
holdsLock(Object obj)	Returns true if and only if the current thread holds the monitor lock on the specified object
interrupt()	Interrupts this thread
interrupted()	Tests whether the current thread has been interrupted
isAlive()	Tests if this thread is alive
isDaemon()	Tests if this thread is a daemon thread
isInterrupted()	Tests whether this thread has been interrupted
join()	Waits for this thread to die
join(long millis)	Waits at most millis milliseconds for this thread to die
run()	If this thread was constructed using a separate Runnable run object, then that Runnable object's run method is called; otherwise, this method does nothing and returns
setContextClassLoader(ClassLoader cl)	Sets the context ClassLoader for this Thread
setDaemon(boolean on)	Marks this thread as either a daemon thread or a user thread
setDefaultUncaughtExceptionHandler( Thread.UncaughtExceptionHandler eh)	Set the default handler invoked when a thread abruptly terminates due to an uncaught exception, and no other handler has been defined for that thread
setName(String name)	Changes the name of this thread to be equal to the argument name.
setUncaughtExceptionHandler( Thread.UncaughtExceptionHandler eh)	Set the handler invoked when this thread abruptly terminates due to an uncaught exception
setPriority(int newPriority)	Changes the priority of this thread
sleep(long millis)	Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds, subject to the precision and accuracy of system timers and schedulers
start()	Causes this thread to begin execution; the Java Virtual Machine calls the run method of this thread
toString()	Returns a string representation of this thread, including the thread's name, priority, and thread group
yield()	A hint to the scheduler that the current thread is willing to yield its current use of a processor