Java Threads | How to create a thread in Java

Multithreading is a fundamental concept in Java programming, allowing developers to execute multiple tasks concurrently within a single program. Threads are lightweight processes that run within the context of a larger process, enabling efficient utilization of system resources and enhancing application responsiveness. In this section, we will explore how to create threads in Java, covering various approaches, best practices.

In Java, threads are represented by instances of the Thread class or by implementing the Runnable interface. The Thread class provides built-in support for multithreading, while the Runnable interface defines a single method, run() that contains the code to be executed by the thread. By implementing the Runnable interface, we can decouple the task from the thread itself, promoting better code organization and reusability.

There are the following two ways to create a thread:

• By Extending Thread Class
• By Implementing Runnable Interface

Thread Class

The simplest way to create a thread in Java is by extending the Thread class and overriding its run() method. Thread class provide constructors and methods to create and perform operations on a thread. Thread class extends Object class and implements Runnable interface.

Constructors of Thread Class

• Thread()
• Thread(String name)
• Thread(Runnable r)
• Thread(Runnable r, String name)

Thread Class Methods

1. public void run(): is used to perform action for a thread.
2. public void start(): starts the execution of the thread.JVM calls the run() method on the thread.
3. public void sleep(long miliseconds): Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds.
4. public void join(): waits for a thread to die.
5. public void join(long miliseconds): waits for a thread to die for the specified miliseconds.
6. public int getPriority(): returns the priority of the thread.
7. public int setPriority(int priority): changes the priority of the thread.
8. public String getName(): returns the name of the thread.
9. public void setName(String name): changes the name of the thread.
10. public Thread currentThread(): returns the reference of currently executing thread.
11. public int getId(): returns the id of the thread.
12. public Thread.State getState(): returns the state of the thread.
13. public boolean isAlive(): tests if the thread is alive.
14. public void yield(): causes the currently executing thread object to temporarily pause and allow other threads to execute.
15. public void suspend(): is used to suspend the thread(depricated).
16. public void resume(): is used to resume the suspended thread(depricated).
17. public void stop(): is used to stop the thread(depricated).
18. public boolean isDaemon(): tests if the thread is a daemon thread.
19. public void setDaemon(boolean b): marks the thread as daemon or user thread.
20. public void interrupt(): interrupts the thread.
21. public boolean isInterrupted(): tests if the thread has been interrupted.
22. public static boolean interrupted(): tests if the current thread has been interrupted.

By Implementing Runnable Interface

Another approach to creating threads in Java is by implementing the Runnable interface. The Runnable interface should be implemented by any class whose instances are intended to be executed by a thread. Runnable interface have only one method named run(). This approach is preferred when we want to separate the task from the thread itself, promoting better encapsulation and flexibility.

public void run(): is used to perform action for a thread.

Starting a Thread

The start() method of the Thread class is used to start a newly created thread. It performs the following tasks:

• A new thread starts (with new callstack).
• The thread moves from New state to the Runnable state.
• When the thread gets a chance to execute, its target run() method will run.

Thread Creation

1) Creating Thread by Extending Thread Class

File Name: Multi.java

Output:

thread is running...

In this example, we define a custom thread by extending the Thread class and overriding the run() method with our desired functionality. We then instantiate the thread and call its start() method to begin execution.

2) Java Thread Example by implementing Runnable interface

FileName: Multi3.java

Output:

thread is running...

In this example, we define a class MyRunnable that implements the Runnable interface and provides the task logic inside its run() method. We then create a new Thread object, passing an instance of MyRunnable to its constructor, and start the thread using the start() method.

If we are not extending the Thread class, the class object would not be treated as a thread object. So, we need to explicitly create the Thread class object. We are passing the object of our class that implements Runnable so that the class's run() method may execute.

3) Using the Thread Class: Thread(String Name)

We can directly use the Thread class to spawn new threads using the constructors defined above.

FileName: MyThread1.java

Output:

My first thread

4) Using the Thread Class: Thread(Runnable r, String name)

Observe the following program.

FileName: MyThread2.java

Output:

My new thread
Now the thread is running ...