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Threads in Java

Java is a popular Object-Oriented Programming language (OOPs) with a feature-rich API and a robust memory management system. One of the key components of this Programming Language is the ability to create and manage Threads in Java. This component can execute multiple tasks concurrently within a single program.   

According to Enlyft, over 455,711 companies worldwide prefer using Java as their primary programming language because of its simplicity and scalability. Threads in Java help simplify tasks for organisations because it enables multiple operations within a single method, making it one of the pillars of Java.

Thus, it is crucial to learn about these key components to learn about the intricacies of Java and master this programming language. So, read this blog to know everything about Threads in Java and take a step forward in your career.

Table of Contents 

1) What is a Thread in Java?

2) What is multitasking in Java?

3) Benefits of using Threads in Java

4) Creating a Thread in Java 

5) Java Thread lifecycle 

6) Priorities of a Java Thread 

7) Java process vs Java Thread – Key differences 

 8) Conclusion 

What is a Thread in Java?

A Thread can be defined as a lightweight sub-process which has its call stack and runs in parallel with other Threads. Thread in Java enables the efficient execution of multiple tasks simultaneously in a single program. Threads can be considered independent, concurrent execution paths within a program.

It can also be defined as the direction, which is taken, while a program is executed. In general, all the programs consist of at least one Thread which is also known as the main Thread. This is provided by Java Virtual Machine or JVM at the beginning, when the program is being executed. At this starting point, when the main Thread is provided, the main () method is invoked, by this same main Thread.

Multitasking in Java is the process where you can perform multiple tasks at the same time. These tasks or processes can be divided into Threads which can be achieved through Multithreading. Let’s discuss the two ways in which multitasking in Java is performed:

a) Process-based multitasking: In this type of Multitasking the processes are heavy and a lot of time is consumed because the program takes a long time to switch between several different processes.

b) Multithreading: This involves the concurrent execution of two or more than two Threads which can be handled in the different parts of the program’s code. Multithreading in Java can be used efficiently for CPU resources, as Threads can run parallel to each other, especially on multi-core processors.
 

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Benefits of using Threads in Java 

There are many benefits to using Threads in Java, including the following: 

a) Efficient use of system resources: By allowing multiple tasks to run concurrently within a single program, Threads in Java can better use available system resources.  

b) Improved program responsiveness: Multithreading can improve a program’ responsiveness, as it allows  you to interact with the program while performing other tasks in the background.  

c) Simplified program structure: By dividing a program into multiple Threads, it becomes easier to manage and maintain.

Creating a Thread in Java

There are two primary ways of creating a Thread in Java which include the following: 

1) Extension of the Thread class: You need to create a new class that extends the Thread class and override the run() method in order to create a new Thread. By extending the Thread class, you can create an instance of this class and start it using the start() method. Here's an example: 
 

public class MyThread extends Thread {
 
  public void run()
{
          System.out.println("Starting MyThread");
 
        for (int i = 0; i < 10; i++)
{
      System.out.println(i);
  
        }
             System.out.println("Ending MyThread");
 
      }
 
  }
    public class Main {
 
      public static void main(String[] args)
{
        MyThread myThread = new MyThread();

        myThread.start();

        System.out.println("Finished");

    }
}


This example creates a new Thread by overriding the run() method and extending the Thread class. The start() method is called to start the Thread, which executes the code in the run() method. 

2) Implementing the runnable interface: To create a new Thread by implementing the runnable interface, you need to create a new class that implements the runnable interface and overrides the run() method. Then, you can create an instance of this class, wrap it in a Thread object, and start the Thread using the start() method. Here's an example: 
 

public class MyRunnable implements Runnable {
 
    public void run()
  {
 
        System.out.println("Starting MyRunnable");
 
        for (int i = 0; i < 10; i++)
  {
 
            System.out.println(i);
 
        }
 
        System.out.println("Ending MyRunnable");
 
    }
 
}
 
public class Main

    public static void main(String[] args)
{
 
        MyRunnable myRunnable = new MyRunnable();
 
        Thread myThread = new Thread(myRunnable);
 
        myThread.start();
 
        System.out.println("Finished");
 
    }
 
}
 


This example creates a new Thread by overriding the run() method and implementing the runnable interface. An instance of this class is created and then wrapped in a Thread object. the start() method is called on the Thread object to start the Thread, which executes the code in the run() method. 

Java Thread lifecycle


Java Thread lifecycle

Java Threads have a defined life cycle consisting of five states: new, runnable, blocked, waiting, and terminated. The Thread goes through these states as it is created, started, and completes its execution. Here's a brief explanation of each state: 

1) New: It is in the new state when a new Thread object is created using the Thread class or by implementing the Runnable interface. At this point, the Thread has not yet started running.

2) Runnable: When the start() method is called on a Thread object, the Thread moves to the runnable state. In the runnable state, the Thread is ready to be scheduled to run by the OS. However, it does not particularly mean that the Thread is currently executing or running.

3) Blocked: A Thread may move to the blocked state if it needs to wait for a currently unavailable resource, such as input or output. The Thread is blocked until the resource becomes available. 

4) Waiting: A Thread may move to the waiting state if it is waiting for a notification from another Thread using the wait() method. The Thread will remain to wait until it receives a notification. 

5) Terminated: A Thread moves to the terminated state when it has completed its execution or has been stopped using the stop() method. Once a Thread is terminated, it cannot be restarted.

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Priorities of a Java Thread

Threads in Java have priorities that are used to determine their relative importance. The Thread priority range is from 1 (lowest) to 10 (highest). By default, all Threads are given a priority of 5. 

The priority of a Thread determines how much CPU time it gets relative to other Threads in the system. Higher-priority Threads are more likely to get CPU time than lower-priority Threads, but there are no guarantees. It is also important to note that Thread priority is just a suggestion to the operating system and is not a hard and fast rule. 

Here's an example to illustrate how Thread priorities work in Java: 
 

public class PriorityExample implements Runnable {
 
    public void run()
{
          for (int i = 1; i <= 10; i++)
  {
              System.out.println(Thread.currentThread().getName() + " - " + i);
 
               }
 
    }
 
    public static void main(String[] args)
 
{
          Thread t1 = new Thread(new PriorityExample(), "Thread 1");
 
        Thread t2 = new Thread(new PriorityExample(), "Thread 2");
 
        t1.setPriority(Thread.MAX_PRIORITY); // set t1 priority to maximum (10)
 
        t2.setPriority(Thread.MIN_PRIORITY); // set t2 priority to minimum (1)
 
           t1.start();
 
        t2.start();
 
    }
 
}


Java process vs Java Thread – Key differences   

A question that often pops up for regular users of Java is how is a Java Process different from a Java Thread. Here is a table that summarises the differences between the both based on different criteria: 
 

Basis of difference 

Java Process 

Java Thread  

 Definition 

An instance of a Java Virtual Machine (JVM) running on a physical or a virtual machine. 

A lightweight unit of execution within a Java Process that shares memory and resources with other Threads within the same process.  

Resource    allocation 

Each Java Process has a memory space of its own and set of system resources the operating system allocates. 

All Java Threads involved within a Process share its memory space and system resources. 

Communication 

Inter-process communication is required for communication between Processes.

Inter-Thread communication can be done using mechanisms such as wait(), notify(), and notifyAll(). 

Context switching 

Context switching between processes is a heavyweight operation that involves saving and restoring the state of the entire process. 

Context switching between Threads is a lightweight operation that saves and restores only the Thread's state. 

 Creation difficulties 

Creating a new Java Process has a relatively high cost regarding memory and system resources. 

Creating a new Java Thread has a relatively low-cost regarding memory and system resources. 

Concurrency 

Processes do not share memory or resources by default, so they must use inter-process communication mechanisms to coordinate their actions. 

Threads share memory and resources within the same process, making coordination and communication between threads easier.  

Scalability 

Creating multiple Java Processes can take up a lot of system resources and may not be scalable for large-scale applications. 

Creating multiple Java Threads within a Process is much more scalable and can be used to support high-concurrency applications.  

Error isolation 

Errors or crashes in one Process do not affect other processes running on the same system. 

Errors or exceptions in one Java Thread can potentially affect other Threads within the same Process. 

Security 

Running each process in its memory space can enhance security by isolating code and data. 

Threads are more susceptible to security threats, like malicious code, that can affect other Threads in the Process.  


Conclusion 

In conclusion, Java Threads in Java are a powerful components of the Java programming language that allows for the concurrent execution of code. They provide a way to execute multiple tasks simultaneously, which can lead to significant performance improvements in applications that require parallel processing. They provide a powerful mechanism for executing multiple tasks concurrently within a single program. By dividing a program into multiple Threads, we can better use system resources, improve program responsiveness and simplify the automation of processes.   

With this blog, we hope you understand Java Threads in detail, how to create and manage Threads, and the main points of distinction between Java Processes and Java Threads.

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An example of Thread in Java is implementing runnable interface.

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Threading in Java is a concept of concurrent execution of two or more than two parts of a program which maximises the utilisation of CPU resources. Each part of such a program is called a “Thread” and each Thread defines a separate path of execution.

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