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Learn Threads in Java with Example

Java threading is one of the most important interview questions, here you will get a brief explanation of why you should use it in your projects with examples.


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Alisha Singh

2 months ago | 10 min read

Learn Threads In Java

When you think of multithreading, your mind probably jumps straight to heavy-duty tasks like processing large data sets and rendering images or videos. 

It’s not surprising that these are the typical uses for multithreaded programs; they’re also some of the most common examples of tasks that would benefit from being handled by more than one thread at a time. However, as programmers who understand the principles behind Thread know, almost any program can take advantage of multiple threads operating simultaneously. 

Even if you don’t have a particularly heavy task at hand, there are still numerous benefits to using Java threading to make several parts of your code operate independently from one another. 

In this article, we will look at what exactly Java threading is and why you should use it in your own projects with examples.

What Is Threading?

In computer programming, threading is the concurrent execution of computer programs, i.e. running more than one program at a time. This can be done as a method of increasing efficiency, for example in a management system in which each employee’s work is split into discrete tasks which can be performed at the same time, instead of requiring each to finish one task before moving on to the next. Threading is one of the most important concepts in programming because it helps us write more efficient code. In fact, most modern programming languages have built-in support for threading, making it easier to write efficient code.

Why is Threading Important?

The most obvious reason that you might want to use threading in your Java programs is to increase their speed. If you are running a program that calculates some data, for instance, you may want to split that process across a few threads so that the rest of your program doesn’t have to wait while the data is being calculated.

The main benefits of using threading in your code are efficiency and scalability. When you split a program’s tasks across several threads, you can make the most of the processing power of your computer. And, if you add more computers to the network that your program is running on, you can easily scale up your program to take advantage of the extra power. Check out important interview questions asked on threads.

Java Threading Basics

When you use Java threading, the program is broken down into discrete parts, each of which is called a “thread”. The way that threads work is that the computer’s operating system (OS) splits the computer’s processor time between the different threads running in your program. When one thread needs to wait for something (such as data being retrieved from a database), the others can continue to process, which means overall efficiency is increased. The OS keeps track of the threads running in a program, as well as which parts of the code are being executed in each thread. When you call a method in your Java threading, the computer uses an OS function called a “context switch” to interrupt the thread currently running and switch to the other thread. When the threads are switched back to the first one, it continues executing where it left off. Next we will discuss some key concepts and functions for using threading in Java before moving to examples.

Runnable and the run() method

A Runnable object can be created from any class. It specifies a task that can be run by a thread when no other thread has been scheduled for execution. It could be a piece of code that performs some lengthy process that should not be attempted when the program is waiting for a user event. A Runnable object can be executed by any Thread. 

The run() method is the entry point of the task specified by the Runnable. The keyword void used as the return type of the run() method specifies that the method does not return any values. By default, the Thread executing the task will start executing the run() method from the beginning. However, you can mark the run() method as being eligible for concurrent execution by using the mark() method.

The main() method

The main() method is the entry point to a Java program. A Java program usually starts with the main() method. A Java application can have many threads. You can create multiple threads and use them to perform various tasks. The main() method is invoked when the Java program starts. It is important to remember that the main() method is a static method. It is not associated with any object. The main() method is the only method that can be executed when the program starts. All other methods are invoked when a thread starts. You must code the main() method as follows: 

public static void main(String[] args)

{

}

The main() method is a static method. Also, there is no “this” in the main() method and the main() method is executed in the same thread that invokes the program. You can use the main() method to create multiple threads and perform various tasks.

Create a Thread in Java

A thread is a sequence of instructions that is executed by a processor as part of a program. Each thread can perform a sequence of instructions asynchronously with respect to other threads. Each thread has its own call stack, local variables, and execution path. There can be a single thread of execution or many threads of execution within a program. In Java, a thread is known as a “Java thread” or a “Java virtual thread”. To create a thread in Java, you will write a “new Thread” statement, followed by the instructions that the thread should execute once it has been started by the OS.

You can also give a thread a name, and then use the name of the thread instead of the object reference when you want to wait for the thread to finish executing. You will see this in action in our examples.

The main method that is called when a new Java application starts is not a thread.

When you run multiple threads, they share resources like memory and files with one another. The operating system schedules them so that each has its turn to run. This is how your computer can handle several programs at once.

The code below shows how to create a new Java Thread:

public class ThreadTest {

public static void main(String[] args) {

// This line creates a new Java thread called "MyThread"

Thread MyThread = new Thread(new Runnable()

{

public void run() {

System.out.println("MyThread!");

}

});

MyThread.start();

}

}

This code creates a “Runnable” class that contains a single line of code to print "MyThread!" to the console. The code then creates a new Java Thread called "MyThread" and starts it running by calling the start() method. When you run this code, you should see “MyThread!” printed in your console window.

Synchronization and the Java threading API

The Java threading API offers different ways of synchronizing threads, such as the “synchronized” keyword and the “wait” and “notify” methods. Synchronization is important when working with threads because it ensures that threads don’t collide and cause problems for each other. For example, if two threads run into each other as they’re trying to write to the same file, it could cause the file to be corrupted. Synchronization is used to solve this problem by making sure that the threads are waiting for the other to finish before they take their next action. In computer programming, synchronization is the coordination of activities between concurrent (running) computer processes or threads. This coordination might be achieved by a computer process or thread waiting until another process or thread has completed a given activity, or it might be achieved by two or more computer processes or threads executing their activities strictly in sequence.

Key synchronization functions:

sleep():

  • You can use the sleep() method to make a thread sleep for a specified amount of time. 
  • The sleep() method does not halt the execution of the thread; instead, it just schedules the current thread for interruption at the specified time. 

wait():

  • The wait() method can be used to synchronize the execution of multiple threads and avoid the situation where a thread interferes with another thread and vice versa.
  • The wait() method is used to halt the execution of a thread till another execution completes. 
  • The thread that executes the wait() method is known as the blocked thread. 

interrupt():

  • The interrupt() method is used to interrupt the execution of a thread. 
  • The interrupt() method halts the execution of a thread and puts the thread in the blocked state. 

isAlive(): The isAlive() method is used to check if the specified thread is alive or not. 

join(): The join() method is used to wait till another thread completes its execution.

When to Use Java Threading?

Java threading is great to use whenever you have a task that can be broken down into smaller portions that can run simultaneously. This could include something like a program that needs to look through a large data set and find matching items. It could also just be used to preprocess data before you load it into another program. Another good example of when to use Java threading is when you have a program that needs to constantly monitor something, like a stock price that changes several times a day. If you use Java threading, you can split up the code so that it’s constantly checking the stock price and updating the values, so no matter what time of day it is, your program will be able to respond instantly.

Java threading can be used to make your code run faster, but only if you have a program that is doing more than one thing at once. For example, if you have a program that does nothing but print “Hello World!” on the screen, then using Java threading probably won’t make your code run any faster. This is because the computer doesn’t need to do more than one thing at once. It simply needs to print “Hello World!” on the screen and then wait for you to tell it what to do next. With this lets discuss some more limitations of the threading in Java in the next section.

Limitations of Threading in Java

Sometimes, Java threading doesn’t work as well as we’d like it to, and that’s when you may want to consider using another programming language. For example, if you are working with image editing, it is important to process the algorithms in your code as a series of discrete steps. This can be challenging in Java because its threading model assumes that these steps can be interrupted at any time, which might not be what you want at all when dealing with an image. That’s why professional image editors use other programming languages that are better suited to this type of multithreaded processing.

Another example is when you need to share data between threads. If you have a program that uses multiple threads, it can be really tricky to share data between them. The best way to do this is by using something called a shared variable, which is basically a variable that both threads can access at the same time without any problems. The problem with this is that it’s easy for one thread to accidentally change the value of the shared variable while another thread is trying to use it, which could cause all kinds of errors in your code.

Java threading can also be hard if you don’t know much about programming. For example, if you use Java threading and try to write your own code for how each thread should run and how they should communicate with each other, there’s a good chance that you will make mistakes and end up creating bugs in your program. This is why many programmers prefer using something called an “event-driven” model, which means they rely on programs like Java Swing or Java GUI components instead of writing their own code to handle events like keystrokes or mouse clicks.

Synchronization between Threads

Synchronization between threads is done through the use of “synchronized” blocks of code, which is a way of restricting access to certain parts of the program to only one thread at a time. This is particularly useful when you have data that multiple threads need to access, but you don’t want them to be able to change it at the same time. For example, let’s say that you have a program that is collecting data from multiple sources, and you want to make sure that the data from each of those sources is stored in the same file. If you don’t use synchronization, it would be easy for one thread to accidentally overwrite the data that the other thread has just written. Once you have the data in the file, though, you can synchronize access to the file so that only one thread can make changes to it at a time.

Java Thread Examples:

  1. Extending Thread class

class MyThreadClass extends Thread{

public void run(){

System.out.println("My thread class run method is running...");

}

public static void main(String args[]){

MyThreadClass myThreadObject = new MyThreadClass();

myThreadObject.start();

} }

Output: My thread class run method is running.

2.Implementing Runnable interface

class MyThreadClass implements Runnable{

public void run(){

System.out.println("My thread class run method is running...");

}

public static void main(String args[]){

MyThreadClass myThreadObject=new MyThreadClass();

Thread threadObject =new Thread(myThreadObject); // Using the constructor Thread(Runnable r)

threadObject.start();

} }

Output: My thread class run method is running...

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

public class MyThreadClass {

// Main method

public static void main(String args[]) {

// now we will create an object of the Thread class via the constructor Thread(String name)

Thread threadObject= new Thread("My thread class object");

// the start() method moves the thread to the active state

threadObject.start();

// get the thread name by calling the getName() method

String myString = threadObject.getName();

System.out.print(myString);

} }

Output: My thread class object

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

public class MyThreadClass {

// Main method

public static void main(String args[]) {

// now we will create an object of the Thread class via the constructor Thread(String name)

Thread threadObject= new Thread("My thread class object");

// the start() method moves the thread to the active state

threadObject.start();

// get the thread name by calling the getName() method

String myString = threadObject.getName();

System.out.print(myString);

} }

Output: My thread class run method is running...

Conclusion

Threading is a great way to improve the efficiency of your code, but it can also introduce some issues if it isn’t used properly. When writing multithreaded programs, it’s important to consider things like how you’re going to synchronize access to shared data, as well as how you’re going to deal with errors that can occur in one thread but not others. For the most part, though, Java threading is an incredibly powerful tool that can make your programs run much more efficiently, be more scalable, and operate more quickly than they would if they weren’t threaded.

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Alisha Singh


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