4 Reasons and Benefits of Using Multithreading in Java? Why Threads?

In one word, we use Threads to make Java applications faster by doing multiple things at the same time. In technical terms, Thread helps you to achieve parallelism in Java programs. Since CPU is very fast and nowadays it even contains multiple cores, just one thread is not able to take advantage of all the cores, which means your costly hardware will remain idle for most of the time. By using multiple threads, you can take full advantage of multiple cores by serving more clients and serving them faster. Since, in today's fast-paced world, response time matters a lot and that's why you have multi-core CPUs, but if your application doesn't make full use of all resources then there is no point adding them, multi-threading is one way to exploiting huge computing power of CPU in Java application.

There is one more purpose of using Thread in Java, to do multiple tasks simultaneously. For example, in the GUI application, you want to draw screens at the same time you also want to capture the user's action e.g. pressing keys and commands and you may want to download or uploading something from the network.

If you do all these tasks in one thread, they would be executed sequentially i.e. first you draw the screen then you capture the command and finally you upload your high score to the network. 

This may cause a problem for your game or application because GUI seems to be frozen while you doing another task. 

By using multiple threads in Java you can execute each of these tasks independently.

And, if you are serious about mastering Java multi-threading and concurrency then I also suggest you take a look at these advanced Java Multithreading courses from Udemy and Coursera It's an advanced course to become an expert in Multithreading, concurrency, and Parallel programming in Java with a strong emphasis on high performance.

Reasons for using Multithreading in Java

Even Java application contains at least one thread, which is called the main thread which executes your main method. There are more threads used by JVM like daemon threads which do garbage collections and some other housekeeping works. 

As an application developer, you can also add new user threads to make your application faster and more efficient. Here are a couple of common reasons and scenarios to use multiple threads in Java:

1.  Parallel Programming

One of the main reasons to use threads in Java is to make a task run parallel to another task like drawing and event handling. GUI applications e.g. Swing and Java FX GUIs are the best examples of multi-threading in Java. 

In a typical GUI application, the user initiates an action like downloading a file from the network or loading games modules from a hard disk.

These actions require some time to complete but you cannot freeze the GUI because then the user will think your application is hung. 

Instead, you need a separate thread to carry out the time-consuming task and keep showing relevant messages to the user or allow him to do other tasks at the same time to keep your GUI alive. This is achieved by using multiple threads in Java.

2. To take full advantage of CPU power.

Another common reason for using multiple threads in Java is to improve the throughput of the application by utilizing full CPU power. 

For example, if you have got 32 core CPUs and you are only using 1 of them for serving 1000 clients and assuming that your application is CPU bound, you can improve throughput to 32 times by using 32 threads, which will utilize all 32 cores of your CPU.

You can further read a good book on Java performance tuning books like Java Performance The Definitive Guide  By Scott Oaks to learn more about the performance impact of multi-threading.

3. For reducing response time

You can also use multiple threads to reduce response time by doing fast computation by dividing a big problem into smaller chunks and processing them by using multiple threads. 

For example, the map-reduce pattern is based upon dividing a big problem into smaller ones and processing them individually, Java also provides Fork-Join Thread pool for just that purpose.

4. To sever multiple clients at the same time.

One of the most common scenarios where using multiple threads significantly improves an application's performance is a client-server application. 

A single-threaded application means only one client can connect to the server at a time, but a multi-threaded server means multiple clients can connect to the server at the same time. 

This means the next client doesn't have to wait until your application finish processing the request of the previous client. 

Like in the following example, you can see that multiple requests are processing by our multi-threaded server at the same time.

By the way, Threading is not free, it comes with its own challenges. You can only maximize the throughput of your application up to a certain extent, once the numbering of the thread increases up to a certain threshold, they will start competing for CPU, and context switching will occur. 

Context switching means one thread that is using CPU is suspended and the CPU is allocated to another thread for execution. When this happens, the thread generally loses all of its cached data. If that thread resumes on another core then it has to build its cache from the start.

Threading also introduces a special set of a problem known as multi-threading issue e.g. deadlock, livelock, memory inconsistency error, race conditions, and starvation.

It's also very difficult to test a Java program that involves multiple threads. You cannot predict the order of execution in the case of multi-threading and without any synchronization. You should also read Java Concurrency in Practice to learn more about how to use threads effectively in Java.

Also, parallelism will be limited to the fact of the size of critical section i.e. the part of the code which must be executed by the only thread at a time. If you have a long critical section then eventually all threads will wait there and your program will behave like a single-threaded program.


That's all about why use Threads in Java and the benefits of Multithreading in Java. The fundamental of using a thread is the same as using multiple workers to complete a task, but you must remember that not all tasks can be completed early by just deploying multiple workers like 9 mothers cannot deliver a baby in one month. Similarly, just creating multiple threads to make your program faster will not work.

You can only improve performance by dividing CPU-bound tasks into multiple threads e.g. large computations. If your application is IO bound, then you may need to think about other techniques e.g. faster hard disk to improve performance.

You should also consider problems associated with multi-threading because handling synchronization between multiple threads and preventing issues like deadlock, livelock, starvation, and memory inconsistency issues are not easy. 

Often a single thread is what you need because it makes coding easy, you don't need to synchronize anything if your application is single-threaded.

I suggest you read a good book on multi-threading and design like Java Concurrency in Practice to learn more about the risk and rewards of using multiple threads in Java.


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