Imagine that you have a sign-in system. However, for each sign-in, it takes half a second to complete. If ten people sign in, it would take five seconds to finish. For a hundred, it would take fifty seconds, and so forth. The run time would increase at a horribly fast rate if the sign-ins were processed one at a time.

But what if we wanted to process all of these sign-ins at the same time? We can solve this problem with multithreading. Multithreading is essentially the use of two or more threads at the same time in order to run a certain process concurrently.

(NOTE : this does not mean that an infinite number of sign-ins will all be processed in 0.5 seconds, as that requires an infinite number of processor cores.)

First, let’s create a dummy sign in class.

public class SignInRequest{
  public static void handleSignInRequest(){
    //insert magical logic here
  }
}

And then make a Request class using the Observer pattern, so that we can create a RequestListener afterwards.

Now, let’s create a new thread that we can run whenever we get a sign-in request.

public class SignInThread extends Thread{

  private SignInRequest request;

  public SignInThread(SignInRequest request){
    this.request = request;
  }
  public void run(){
    request.handleSignIn();
  }
}

At this point, we can use this SignInThread whenever we get a request.

public void onGetRequest(){
  SignInThread thread = new SignInThread();
  thread.start();
}

It is important that you run the start() method and not the run method.

By doing this, we can handle hundreds of sign in request concurrently, making the sign in process much faster.

In particular, threads are powerful when used with a computer with multiple cores.

For example, if you have 100 sign in requests, and multiple processor cores, you can split the sign ins between the cores by creating multiple threads. This means all of your cores can work at full-speed, whereas only one core would be used if it was not multithreaded.

However, you can multithread with a single core as well. However, when you only have one core, multithreading will not give any speed boosts, and it would be practically the same as if your code was single-threaded.

The most well-known use for multithreading is when you have a GUI. Consider a GUI program that calculates giant numbers. What happens if the calculation takes 30 seconds, and you decide to cancel the calculation? If the program only had a single-thread, this task would be impossible. The user cannot click the cancel button until the calculations are done. However, if it is multithreaded, then the calculations are completely separate from everything else. As a result, the user would be able to click the cancel button, since the calculations are done on a separate thread.

Multiple threads, with multiple cores, will cause your code to run much faster. Faster code, higher efficiency, and the ability to multitask. What’s not to like?