In this article, we will discuss important methods and constructors of a Thread class

1. Thread :

Thread is a separate flow of execution in a program/process
Threads are light–weight processes or smallest unit of work in a process
Creating a Thread or spawning a new Thread means allocating a separate independent flow of execution in a process
So, we can create as many as Threads required for the process/program or in other way a process can contain multiple threads independent of each other
Multiple threads of the same process share memory address of that process allowing inter–process communication faster and context–switching less expensive

1.1 Creating a Thread :

There are 2 ways to create a Thread in Java,

By extending Thread class
By implementing Runnable interface

In both the ways, run() method has to be implemented providing the logic/work that separate thread need to be executed

MyThread.java

public class MyThread extends Thread {

	@Override
	public void run() {
		// work for new thread
	}
}

MyRunnable.java

public class MyRunnable implements Runnable {

	@Override
	public void run() {
		// work for new thread
	}
}

2. Thread Constructors :

There are 8 constructors defined in Thread class, those are –

2.1 Thread t = new Thread();

Allocates a new Thread object

ThreadConstructor1.java

package in.bench.resources.threads;

public class ThreadConstructor1 {

	public static void main(String[] args) {

		// create Thread - not started
		Thread t = new Thread();

		// print below values
		System.out.println("Id= " + t.getId());
		System.out.println("Priority= " + t.getPriority());
		System.out.println("Name= " + t.getName());
		System.out.println("State= " + t.getState());
		System.out.println("Thread Group= " + t.getThreadGroup());
		System.out.print("Current executing thread name= " + Thread.currentThread().getName());
	}
}

Output :

Id= 15
Priority= 5
Name= Thread-0
State= NEW
Thread Group= java.lang.ThreadGroup[name=main,maxpri=10]
Current executing thread name= main

2.2 Thread t = new Thread(Runnable r);

Allocates a new Thread object

ThreadConstructor2.java

package in.bench.resources.threads;

public class ThreadConstructor2 {

	public static void main(String[] args) {

		// create instance of Runnable
		MyRunnable r = new MyRunnable();

		// create Thread passing Runnable instance - not started
		Thread t = new Thread(r);

		// print below values
		System.out.println("Id= " + t.getId());
		System.out.println("Priority= " + t.getPriority());
		System.out.println("Name= " + t.getName());
		System.out.println("State= " + t.getState());
		System.out.println("Thread Group= " + t.getThreadGroup());
		System.out.print("Current executing thread name= " + Thread.currentThread().getName());
	}
}

Output :

Id= 15
Priority= 5
Name= Thread-0
State= NEW
Thread Group= java.lang.ThreadGroup[name=main,maxpri=10]
Current executing thread name= main

2.3 Thread t = new Thread(String name);

Allocates a new Thread object

ThreadConstructor3.java

package in.bench.resources.threads;

public class ThreadConstructor3 {

	public static void main(String[] args) {

		// create Thread - not started
		Thread t = new Thread("bench3");

		// print below values
		System.out.println("Id= " + t.getId());
		System.out.println("Priority= " + t.getPriority());
		System.out.println("Name= " + t.getName());
		System.out.println("State= " + t.getState());
		System.out.println("Thread Group= " + t.getThreadGroup());
		System.out.print("Current executing thread name= " + Thread.currentThread().getName());
	}
}

Output :

Id= 15
Priority= 5
Name= bench3
State= NEW
Thread Group= java.lang.ThreadGroup[name=main,maxpri=10]
Current executing thread name= main

2.4 Thread t = new Thread(Runnable r, String name);

Allocates a new Thread object

ThreadConstructor4.java

package in.bench.resources.threads;

public class ThreadConstructor4 {

	public static void main(String[] args) {

		// create instance of Runnable
		MyRunnable r = new MyRunnable();

		// create Thread - not started
		Thread t = new Thread(r, "bench4");

		// print below values
		System.out.println("Id= " + t.getId());
		System.out.println("Priority= " + t.getPriority());
		System.out.println("Name= " + t.getName());
		System.out.println("State= " + t.getState());
		System.out.println("Thread Group= " + t.getThreadGroup());
		System.out.print("Current executing thread name= " + Thread.currentThread().getName());
	}
}

Output :

Id= 15
Priority= 5
Name= bench4
State= NEW
Thread Group= java.lang.ThreadGroup[name=main,maxpri=10]
Current executing thread name= main

2.5 Thread t = new Thread(ThreadGroup tg, String name);

Allocates a new Thread object

ThreadConstructor5.java

package in.bench.resources.threads;

public class ThreadConstructor5 {

	public static void main(String[] args) {

		// create instance of ThreadGroup
		ThreadGroup tg = new ThreadGroup("threadgroup5"); 

		// create Thread - not started
		Thread t = new Thread(tg, "thread5");

		// print below values
		System.out.println("Id= " + t.getId());
		System.out.println("Priority= " + t.getPriority());
		System.out.println("Name= " + t.getName());
		System.out.println("State= " + t.getState());
		System.out.println("Thread Group= " + t.getThreadGroup());
		System.out.print("Current executing thread name= " + Thread.currentThread().getName());
	}
}

Output :

Id= 15
Priority= 5
Name= thread5
State= NEW
Thread Group= java.lang.ThreadGroup[name=threadgroup5,maxpri=10]
Current executing thread name= main

2.6 Thread t = new Thread(ThreadGroup tg, Runnable r);

Allocates a new Thread object

ThreadConstructor6.java

package in.bench.resources.threads;

public class ThreadConstructor6 {

	public static void main(String[] args) {

		// create instance of Runnable
		MyRunnable r = new MyRunnable();

		// create instance of ThreadGroup
		ThreadGroup tg = new ThreadGroup("threadgroup6"); 

		// create Thread - not started
		Thread t = new Thread(tg, r);

		// print below values
		System.out.println("Id= " + t.getId());
		System.out.println("Priority= " + t.getPriority());
		System.out.println("Name= " + t.getName());
		System.out.println("State= " + t.getState());
		System.out.println("Thread Group= " + t.getThreadGroup());
		System.out.print("Current executing thread name= " + Thread.currentThread().getName());
	}
}

Output :

Id= 15
Priority= 5
Name= Thread-0
State= NEW
Thread Group= java.lang.ThreadGroup[name=threadgroup6,maxpri=10]
Current executing thread name= main

2.7 Thread t = new Thread(ThreadGroup tg, Runnable r, String name);

Allocates a new Thread object so that –
1. It has target as its run object
2. Has the specified name as its name
3. Belongs to the thread group referred to by group

ThreadConstructor7.java

package in.bench.resources.threads;

public class ThreadConstructor7 {

	public static void main(String[] args) {

		// create instance of Runnable
		MyRunnable r = new MyRunnable();

		// create instance of ThreadGroup
		ThreadGroup tg = new ThreadGroup("threadgroup7"); 

		// create Thread - not started
		Thread t = new Thread(tg, r, "thread7");

		// print below values
		System.out.println("Id= " + t.getId());
		System.out.println("Priority= " + t.getPriority());
		System.out.println("Name= " + t.getName());
		System.out.println("State= " + t.getState());
		System.out.println("Thread Group= " + t.getThreadGroup());
		System.out.print("Current executing thread name= " + Thread.currentThread().getName());
	}
}

Output :

Id= 15
Priority= 5
Name= thread7
State= NEW
Thread Group= java.lang.ThreadGroup[name=threadgroup7,maxpri=10]
Current executing thread name= main

2.8 Thread t = new Thread(ThreadGroup tg, Runnable r, String name, long stackSize);

Allocates a new Thread object so that –
1. It has target as its run object
2. Has the specified name as its name
3. Belongs to the thread group referred to by group
4. Has the specified stack size

ThreadConstructor8.java

package in.bench.resources.threads;

public class ThreadConstructor8 {

	public static void main(String[] args) {

		// create instance of Runnable
		MyRunnable r = new MyRunnable();

		// create instance of ThreadGroup
		ThreadGroup tg = new ThreadGroup("threadgroup8"); 

		// create Thread - not started
		Thread t = new Thread(tg, r, "thread8", 88);

		// print below values
		System.out.println("Id= " + t.getId());
		System.out.println("Priority= " + t.getPriority());
		System.out.println("Name= " + t.getName());
		System.out.println("State= " + t.getState());
		System.out.println("Thread Group= " + t.getThreadGroup());
		System.out.print("Current executing thread name= " + Thread.currentThread().getName());
	}
}

Output :

Id= 15
Priority= 5
Name= thread8
State= NEW
Thread Group= java.lang.ThreadGroup[name=threadgroup8,maxpri=10]
Current executing thread name= main

3. Thread Methods :

In this section, we will cover important methods of Thread class –

getName()
- returns invoking thread‘s name
setName(String name)
- Changes the name of the invoking thread with the supplied/passed argument name
getPriority()
- returns invoking thread‘s priority
setPriority(int newPriority)
- Changes the priority of the invoking thread
getId()
- returns the identifier of the invoking thread
getState()
- returns the state of the invoking thread
getThreadGroup()
- returns the thread group to which the invoking thread belongs
isDaemon()
- Checks whether the invoking thread is a daemon thread
setDaemon(boolean on)
- Marks/sets the invoking thread as either a daemon thread or a user thread based on true/false value supplied/passed as method–argument
currentThread()
- returns a reference to the currently executing thread object
activeCount()
- returns an estimate of the number of active threads in the current thread‘s thread group and its sub-groups
clone()
- Throws CloneNotSupportedException as a Thread can not be meaningfully cloned
isInterrupted()
- Tests whether the invoking thread has been interrupted
interrupted()
- Tests whether the current thread has been interrupted
interrupt()
- Interrupts the invoking thread
isAlive()
- Tests whether the invoking thread is alive
run()
- If the invoking 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
start()
- Causes the invoking thread to begin execution; the Java Virtual Machine (JVM) calls the run method of invoking thread
join() – there are 3 variants of join() method
- join() – waits for the invoking thread to die
- join(long millis) – waits at most millis milliseconds for the invoking thread to die
- join(long millis, int nanos) – waits at most millis milliseconds plus nanos nanoseconds for the invoking thread to die
sleep() – there are 2 variants of sleep() method
- 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
- sleep(long millis, int nanos) – causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds plus the specified number of nanoseconds, subject to the precision and accuracy of system timers and schedulers
yield()
- A hint to the scheduler that the current thread is willing to yield its current use of a processor/CPU
Below methods are deprecated –
- destroy()
- stop()
- resume()
- suspend()
Below methods are inherited from class java.lang.Object –
- equals()
- finalize()
- getClass()
- hashCode()
- notify()
- notifyAll()
- wait()

We will see examples for few of the above mentioned methods

3.1 Setting & Getting Thread Names :

setName(String) –
- This method changes/sets/modifies the thread name with passed/supplied value
getName() –
- This method returns the thread name which could be default JVM provided name or explicitly set/modified by the programmer

ThreadNameDemo.java

package in.bench.resources.threads;

public class ThreadNameDemo {

	public static void main(String[] args) {

		// 1. create Thread - not started
		Thread t = new Thread();


		// 2. get current name of the name
		String name = t.getName(); // default JVM provided
		System.out.println("1. Current Thread Name = " + name);


		// 3. set the name of the Thread
		t.setName("Bench");


		// 4. again, get the name of the Thread
		name = t.getName();
		System.out.print("\n2. After changing Thread Name = " + name);
	}
}

Output :

1. Current Thread Name = Thread-0

2. After changing Thread Name = Bench

3.2 Setting & Getting Thread Priority :

setPriority(int) –
- This method changes/sets/modifies the invoking thread priority with passed/supplied value
getPriority() –
- This method returns the thread priority of the invoking Thread which could be default JVM provided priority or explicitly set by the programmer

ThreadPriorityDemo.java

package in.bench.resources.threads;

public class ThreadPriorityDemo {

	public static void main(String[] args) {

		// 1. create Thread - not started
		Thread t = new Thread();


		// 2. get thread priority
		int priority = t.getPriority(); // default JVM provided
		System.out.println("1. Current Thread Priority = " + priority);


		// 3. set the priority of the Thread
		t.setPriority(7);


		// 4. again, get the priority of the Thread
		priority = t.getPriority();
		System.out.print("\n2. After changing Thread Priority = " + priority);
	}
}

Output :

1. Current Thread Priority = 5

2. After changing Thread Priority = 7

3.3 Checking & Setting Daemon Thread :

isDaemon() –
- Checks whether the invoking thread is a daemon thread
setDaemon(boolean) –
- Marks/sets the invoking thread as either a daemon thread or a user thread based on true/false value passed as method–argument

DaemonThreadDemo.java

package in.bench.resources.threads;

public class DaemonThreadDemo {

	public static void main(String[] args) {

		// 1. create Thread - not started
		Thread t = new Thread();


		// 2. check Thread is daemon
		boolean isDaemon = t.isDaemon(); // default JVM provided
		System.out.println("1. Current Thread is daemon ? = " + isDaemon);


		// 3. set the Thread to Daemon
		t.setDaemon(true);


		// 4. again, get the priority of the Thread
		isDaemon = t.isDaemon();
		System.out.print("\n2. After setting Thread to Daemon = " + isDaemon);
	}
}

Output :

1. Current Thread is daemon ? = false

2. After setting Thread to Daemon = true

3.4 Check State of the Thread :

getState() –
- returns the state of the invoking thread
Different Thread State are –
1. NEW
2. RUNNABLE
3. BLOCKED
4. WAITING
5. TIMED_WAITING
6. TERMINATED

ThreadStateDemo.java

package in.bench.resources.threads;

import java.lang.Thread.State;

public class ThreadStateDemo {

	public static void main(String[] args) {

		// 1. create Thread - not started
		Thread t = new Thread();


		// 2. check thread state
		State state = t.getState(); // initial state provided by JVM
		System.out.print("Current Thread State is = " + state);
	}
}

Output :

Current Thread State is = NEW

3.5 Get current executing Thread :

currentThread()
- returns a reference to the currently executing thread object

GetCurrentExecutingThread.java

package in.bench.resources.threads;

public class GetCurrentExecutingThread {

	public static void main(String[] args) {

		// 1. get current executing Thread
		Thread currentThread = Thread.currentThread();
		System.out.println("1. Current Thread details = " + currentThread);


		// 2. get name of the current executing Thread
		String currentThreadName = Thread.currentThread().getName();
		System.out.print("\n2. Current Thread name is = " + currentThreadName);
	}
}

Output :

1. Current Thread details = Thread[main,5,main]

2. Current Thread name is = main

3.6 Get Id & ThreadGroup of current executing Thread :

getId()
- returns the identifier of the invoking Thread
getThreadGroup()
- returns the thread group to which the invoking thread belongs

GetIdAndStateOfCurrentExecutingThread.java

package in.bench.resources.threads;

public class GetIdAndStateOfCurrentExecutingThread {

	public static void main(String[] args) {

		// 1. get current executing Thread
		Thread currentThread = Thread.currentThread();
		System.out.println("1. Current Thread details = " + currentThread);


		// 2. get Id of the current executing Thread
		long currentThreadId = Thread.currentThread().getId();
		System.out.println("\n2. Id of Current Thread is = " + currentThreadId);


		// 3. get Id of the current executing Thread
		String currentThreadGroup = Thread.currentThread().getThreadGroup().getName();
		System.out.print("\n3. Current Thread Group is = " + currentThreadGroup);
	}
}

Output :

1. Current Thread details = Thread[main,5,main]

2. Id of Current Thread is = 1

3. Current Thread Group is = main

3.7 Interrupting a Thread :

isInterrupted()
- Tests whether the invoking thread has been interrupted
interrupted()
- Tests whether the current thread has been interrupted
interrupt()
- Interrupts the invoking thread

ThreadInterruptionDemo.java

package in.bench.resources.threads;

public class ThreadInterruptionDemo {

	public static void main(String[] args) {

		// 1. create Thread - not started
		Thread t = new Thread();


		// 2. check whether Thread t is interrupted
		boolean isInterrupted = t.isInterrupted();
		System.out.println("1. Thread t is Interrupted ? = " + isInterrupted);


		// 3. check current Thread is interrupted
		boolean interrupted = Thread.currentThread().interrupted();
		System.out.println("\n2. Current executing Thread is Interrupted ? = " + interrupted);


		// 4. interrupt the Thread t
		t.interrupt();


		// 5. again, check whether Thread t is interrupted
		isInterrupted = t.isInterrupted();
		System.out.println("\n3. Again, Thread t is Interrupted ? = " + isInterrupted);


		// 6. interrupt the current executing Thread
		Thread.currentThread().interrupt();


		// 7. check current Thread is interrupted
		interrupted = Thread.currentThread().interrupted();
		System.out.print("\n4. Current executing Thread is Interrupted ? = " + interrupted);
	}
}

Output :

1. Thread t is Interrupted ? = false

2. Current executing Thread is Interrupted ? = false

3. Again, Thread t is Interrupted ? = true

4. Current executing Thread is Interrupted ? = true

Java – Introduction to Threads
Java – Different ways to create/spawn a Thread
Java – Thread Scheduler
Java – Important methods and constructors of a Thread class
Java – Difference between start() and run() methods of Thread class
Java – Importance of start() method in Thread class
Java – Overloading run() method of Thread class
Java – Effects of not overriding run() method of Thread class
Java – Setting and getting name of a Thread
Java – Thread priorities

References :

Happy Coding !!
Happy Learning !!

1. Thread :

1.1 Creating a Thread :

MyThread.java

MyRunnable.java

2. Thread Constructors :

2.1 Thread t = new Thread();

ThreadConstructor1.java

Output :

2.2 Thread t = new Thread(Runnable r);

ThreadConstructor2.java

Output :

2.3 Thread t = new Thread(String name);

ThreadConstructor3.java

Output :

2.4 Thread t = new Thread(Runnable r, String name);

ThreadConstructor4.java

Output :

2.5 Thread t = new Thread(ThreadGroup tg, String name);

ThreadConstructor5.java

Output :

2.6 Thread t = new Thread(ThreadGroup tg, Runnable r);

ThreadConstructor6.java

Output :

2.7 Thread t = new Thread(ThreadGroup tg, Runnable r, String name);

ThreadConstructor7.java

Output :

2.8 Thread t = new Thread(ThreadGroup tg, Runnable r, String name, long stackSize);

ThreadConstructor8.java

Output :

3. Thread Methods :

3.1 Setting & Getting Thread Names :

ThreadNameDemo.java

Output :

3.2 Setting & Getting Thread Priority :

ThreadPriorityDemo.java

Output :

3.3 Checking & Setting Daemon Thread :

DaemonThreadDemo.java

Output :

3.4 Check State of the Thread :

ThreadStateDemo.java

Output :

3.5 Get current executing Thread :

GetCurrentExecutingThread.java

Output :

3.6 Get Id & ThreadGroup of current executing Thread :

GetIdAndStateOfCurrentExecutingThread.java

Output :

3.7 Interrupting a Thread :

ThreadInterruptionDemo.java

Output :

Related Articles :

References :

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