What Are Threads in Java?
In Java and other programming languages, a thread is the basic unit of CPU usage. Threads are part of a process. A simple way to think of a process is as a program that is running.
However, this definition is not 100% accurate. A program can have multiple processes. The definition above is just a simple and useful way to think about a process.
As mentioned earlier, processes contain threads. A thread shares the process's data, code, and other resources with the other threads in the same process.
In Java, developers can create multithreaded applications. Multithreading allows parts of your program to run simultaneously or in parallel, thereby significantly improving your application's performance.
It is important to distinguish concurrency from parallelism. A program can run concurrently, but not in parallel.
Concurrency refers to executing multiple parts of the same program (not simultaneously). These different parts are executed through time-slicing. Parallelism, on the other hand, refers to executing multiple parts of the same program simultaneously.
On single-core systems, concurrency can be achieved through interleaving. Parallelism, however, can only be achieved on a multicore system by running multiple threads on different cores.
Threads can also be used to counter the performance overhead that comes with creating a process. This is especially important when it comes to carrying out repetitive tasks that your program needs to perform.
A web server is a good example to demonstrate this. You could have your server create a new process every time a user makes a request. However, this would require the first user to finish before the next user's request could also be processed.
If you used a multithreaded application, your server would simply have a new thread to handle the new request. Since threads share the same process resources, this saves your program from having to allocate new resources and deal with the associated overhead.
How to Implement Threads in Java
There are two ways to use threads in Java applications. The first is to implement the Runnable interface. When you implement this interface, you must provide a body for the run() method in your class. This code will be run by your thread.
It is important to note that creating an instance of the class does not create a thread right away. The thread is created when you call the start() method.
Final Thoughts on Using Threads in Java
This programming tutorial showed how you can use the Java Threads API and the benefits of multithreading. When writing your regular Java applications, you can simply leave thread handling to the JVM.
The JVM usually runs one program thread at a time, which may not be suitable for systems that require speed, such as gaming applications. So, as a programmer, you need to learn how to create multithreaded applications.
