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An Introduction to Thread in Java

In Java, a thread is a path or direction taken during the execution of any program. Any program has a minimum of one thread, better called the main thread. The Java Virtual Machine or JVM provides it at the beginning of any program's execution. After the main thread is offered, its main thread will involve the prime method.

What are Threads in Java? 

Wondering what are threads in Java? Well, threads are the execution threads in programs. In short, multiple threads of execution might get run by the application that runs on the JVM. The prime focus of individual threads varies depending on certain parameters. The higher-priority threads will be executed before the lower ones.

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How Threads Work in a Multithreading Environment in Java

Multithreading in Java is the concept in the current operating systems. It refers to more than one task executing simultaneously within one program. Multithreading can be achieved in Java using the thread class as well as the runnable interface. Now, what are the runnable interface and thread class? Simply put, Java's runnable interface and thread class allow for creating and controlling a particular thread in Java. The thread class controls any thread in the following ways:

  • It creates the child class, extending the parent Thread class 
  • It declares a class and implements the runnable interface 

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Differences Between Processes and Threads in Java

As we now know the entire lifecycle of a java thread, let us know how threads are created in java. A process is the programs dispatched from a ready state and scheduled in the CPU for the execution process. A process may create other processes that are referred to as the child processes. The process might take time for termination and is isolated. That means it doesn't share the memory with another process. It has several states, such as the following:

  • New
  • Running
  • Ready
  • Waiting
  • Terminated As Well As
  • Suspended

On the contrary, a thread is a segment of the process. So, it is a process with different threads that are contained within the process. In simple terms, the thread has three different states:

  • Running
  • Ready 
  • Blocked

A thread will take less time for termination when compared to the other type. However, unlike the process, they don't isolate. 

These are the major differences between Differences Between Processes and Threads in Java:

 

Processes Threads
Definition An instance of a program running independently A lightweight unit of execution within a process
Memory Each process has its own separate memory space Threads share the same memory space
Communication Inter-process communication is more complex Inter-thread communication is relatively easier
Creation Creation of a new process requires more resources Creating a new thread is less resource-intensive
Overhead Context switching between processes has higher overhead Context switching between threads has lower overhead
Independence Processes are independent of each other Threads are dependent on the parent process
Scalability Processes are more scalable due to independent memory Threads may suffer from contention and scalability issues
Fault Isolation A process crash does not affect other processes A thread crash may lead to the entire process crashing
Parallelism Processes can run in parallel on multi-core systems Threads can take advantage of multi-threading and run in parallel
Synchronization Processes require explicit synchronization mechanisms Threads can use synchronization constructs like locks and monitors

 

Why Use Threads in Java?

What is Static Method in Java? Before learning how to use threads, learn the static method by clicking on the link.

Threads allow programs to operate more effectively by performing a wide range of things concurrently. In short, they can be used for performing complex tasks in the background without the interruption of the main program.

Benefits of Using Java Threads

Learn more about the Life cycle of threads in Java here. As of now, here's presenting the list of benefits of threads in Java:

  • It offers an improved throughput with multiple concurrent computer operations as well as I/O requests within one process.
  • It is a fully symmetric and simultaneous use of processors for computation as well as I/O.
  • If a request is launched on the thread, applications don't freeze nor show "hourglass." The whole application won't block, be pending, or wait for the completion of a request.
  • It comes with improved server responsiveness, with the overall throughput of its server being greater.
  • Threads impose negligible impact on the system resources. Here, threads need less overhead to create, manage, and maintain than any other conventional process.
  • Another benefit is that threads can also be used to make complex applications' structure simpler, including server-class and multimedia applications. Note that simple routines might be written for every activity, and that makes complex programs more seamless to design & code. All in all, it is more adaptive to variations considering the user demands.
  • With the synchronization functions of the thread, it helps offer more enhanced process-to-process communication. Besides, it also shares large amounts of data via separate threads of execution within the same address space, which offers high-bandwidth and low-latency communication between tasks within the application.

Examples of When to Use Java Threads

Any thread in java programs enables a program to operate efficiently by performing multiple things concurrently. Threads are used for performing complex tasks in the background without interrupting a main program. Here are the best example of threads in java:

package com.journaldev.threads;
public class HeavyWorkRunnable implements Runnable {
    @Override
    public void run() {
        System.out.println("Doing heavy processing - START "+Thread.currentThread().getName());
        try {
            Thread.sleep(1000);
            //Get database connection, delete unused data from DB
            doDBProcessing();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("Doing heavy processing - END "+Thread.currentThread().getName());
    }
 
    private void doDBProcessing() throws InterruptedException {
        Thread.sleep(5000);
    }
 
}

Another example is mentioned in the following (extending Thread class)

package com.journaldev.threads;
 
public class MyThread extends thread {
 
    public MyThread(String name) {
        super(name);
    }
 
    @Override
    public void run() {
        System.out.println("MyThread - START "+Thread.currentThread().getName());
        try {
            Thread.sleep(1000);
            //Get database connection, delete unused data from DB
            doDBProcessing();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("MyThread - END "+Thread.currentThread().getName());
    }
 
    private void doDBProcessing() throws InterruptedException {
        Thread.sleep(5000);
    }
    
}

Limitations of Using Java Threads

Here's presenting the list of limitations of using threads in Java:

  • First things first, thread synchronization is the additional overhead to a developer
  • Secondly, it shares the common data around threads that may cause data inconsistency and thread sync problems
  • The next thing to consider is that these threads blocking for resources may be a common issue
  • Challenging to manage codes considering the writing or debugging of codes

Creating and Using Threads in Java

Here's a step-by-step narrative presenting the best way to create and use threads in Java:

Method 1: Extending Java.lang.Thread class

When using the first method, one needs to follow the below-offered steps:

Step 1: First, the thread will be created by the new class extending the thread class

Step 2: It creates the instance of the class

Step 3: The run method includes its functionality that needs to be implemented by the thread

Method 2: Implementing Runnable Interface

So, this is a seamless method to create the thread. Here's presenting the steps to follow:

Step 1: First, it is imperative to create a class 

Step 2: After creating the class, it is imperative to implement a runnable interface and then use the run() method.

Note that the code for executing this thread will be written inside run().

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How to Start and Stop a Thread in Java

To start a thread, you need to call the thread's start(). The JVM calls the run() method of the thread. When you wish to stop any thread from running, you can state by the calling stop() method. The method stops executing the running thread, thereby removing it from a waiting threads pool as well as garbage collection. The thread also moves to the dead state after reaching the end of the method automatically.

Synchronization and Java Thread Safety

Thread safe is the method that can be used by a multitude of threads without the occurrence of problems. Synchronized, on the contrary, means the one thread that operates at a single time.

Java Thread Priority and Scheduling

The number of services assigned to a given thread is referred to as its priority. Any thread generated in Java Virtual Machine will be offered priority. Considering the priority scale, it runs between 1 and 10, where:

  • 1 is the lowest priority
  • 5 is of the standard priority and 
  • 10 is the highest priority

The main priority of a thread is set to 5 by default. Note that every child thread consists of the same priority as the parent thread. The thread priority can be adjusted irrespective of whether it is the user-defined or main thread. One can adjust it using the class's constants as mentioned in the following:

Thread.MIN_PRIORITY;
Thread.NORM_PRIORITY;
Thread.MAX_PRIORITY;

Explanation of Java Thread Pools

The thread pool is the software design pattern that helps accomplish the concurrency of any execution in the computer program. Also referred to as the replicated workers (or even worker-crew model), it maintains multiple threads for tasks allocated for simultaneous execution by a supervising program.

Benefits of Using Java Thread Pools

Thread pools improve the overall performance of any application. What they do is reuse threads & avoid the overhead of creating newer ones every time a task gets executed. They also ensure the tasks are executed timely by queueing them and executing them right as the thread are available.

Common Pitfalls and Mistakes When Using Threads in Java

Want to know the mistakes to avoid while using threads? Discover them from the following points:

  • Not protecting the shared resource or data 
  • Implementing the locking mechanism in the wrong way
  • Mis ordering the locks
  • Lengthy and time-consuming critical sections
  • Not being able to perform routine tasks such as updating data to the cloud, logging data, and more
  • Terminating an application prior to the termination of the background threads
  • Joining the Daemon thread

Best Practices for Writing Thread-Safe Code

To write thread-safe codes, it is imperative to practice the following points:

Reducing the use of the shared data between threads

For multiple threads that need to synchronize, serializing is important, which you can do by using a message queue rather than using locks.

It is better to refrain from nested locks. Note that if they are not implemented, they may create live lock or deadlock issues. For nested locks, the locks may be released or taken in the same hierarchy. 

For spin lock & mutex that will be used in a nested way, it is important to take mutex and then spin lock before releasing in the reverse order.

Conclusion

So, this post has elucidated everything about threads in Java. It has also narrated the benefits, limitations, examples, thread methods in java, and other details of multithreading.

FAQ's

To test and debug multi-threaded Java applications, one needs to debug the session by tapping on the button that mentions RUN. After this, one needs to select DEBUG. After the program has run, both threads are suspended in addIfAbsent. This is the right time to switch between threads; one can even control each thread's execution during this time.
A thread is a process in Java, and there are two types of threads in Java. The first one is the user thread, whereas the second one is the daemon thread. While starting an application, the prime focus is the user thread. One can create different user threads and daemon threads. After the execution of all the user threads, JVM will terminate the program.
While using Java, you can create a thread in two ways. The first is by using the thread class, whereas the second one is by using the runnable interface. If the class extends the thread class, you may create threads by creating the objects first.
A thread in Java is the thread of execution in the program. It is a lightweight process that takes the least or minimum CPU time. It maintains a multi-programming behavior. The best examples of a thread in Java are playing movies, scanning the PC, working on paint, etc. Hero Vired is the most comprehensive platform that offers certified courses on AI, ML, JAVA, and more.
Considering the Java multithreading, a thread will be created in two ways. The first uses the thread class, and the other uses the runnable interface.

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