Difference between Fixed and Cached Thread pool in Java Executor Famework

There are mainly two types of thread pools provided by Javas' Executor framework, one is fixed thread pool, which starts with fixed number of threads and other is cached thread pool which creates more threads if initial number of thread is not able to do the job. The newCachedThreadPool() method is used to create a cached pool, while newFixedThreadPool() is used to construct a thread of fixed size. Cached thread pool executes each task as soon as they are submitted, using an existing thread if its idle or creating new threads otherwise, while in case of fixed thread pool, if more tasks are submitted then idle threads then those task are put into a queue and later executed once any other task has finished.

Difference between fixed and cached thread pool in Java

Here are key difference between a fixed and cached thread pools in Java. 

1. When you submit a task they are immediately executed in cached thread but they can be placed in a queue, if no thread is free in case of fixed thread pool. This means, if you want guaranteed and immediate execution then using a cached thread pool is better option but if you are resource constraint and want to use fixed number of threads then fixed thread pool is a better choice. 

2. You can use Executors.newCachedThreadPool() factory method to create a cached pool in Java and Executors.newFixedThreadPool() to create fixed thread pool.  Bot methods are part of Java Concurrency API and defined in Executors utility class. 

3. Cached thread pool can create more threads if required, but no extra threads are created in fixed thread pool. This means cached thread pool is a better choice if you have resources as it can create and increase number of threads in the pool if load increases but fixed thread pool is a better choice in case of resource constraint environment. 

Example of Fixed Thread Pool

Here is an example of Fixed thread pool in Java:

Example of Cached Thread Pool

Here is an example of cached thread pool in Java:

That's all about how to use fixed and cached thread pools in Java. Both of these thread pools are popular ones and if you have used Executor framework in Java then you have definitely used one of them. In this article, we have learned the key differences between both of them and also learned their strength and weaknesses and how they work. 

If you want to remember the difference then just remember their name, a fixed thread pools means number of threads in the pool is fixed while in case of cached thread pool, number of threads can increase or decrease depending upon load. 

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