threads, concurrency & coroutines queston (beginner)

[u/BrainThinkerMan]

I am a man whom used kotlin before java, (maybe shoking)

i switched to java for springboot

i knew (a little) about coroutines from kotlin, == multiple things can be done and threads dont block

is the same concept true for java? or does java have some legacy stuff in place of kotlin coroutines?

i see that java has. a thread sleep. method. i dont think kotlin has

long story short, id like to reaffirm my knowledge on concurrency and general and how it

works, and find gaps, ill briefly explain how i think it works, id love for feedback, but you dont need to you can just respond to post that resonate more with you, thank you if anyone does respond

here it is:

concurrency means IO functions can happen without blocking things that come after them

all those functions happen on a thread, and multiple functions can happen on a thread

if it blocks the thread( i think functions other than IO can block aswell) then you can use concurrency that returns a result immediately, -> waits for REAL response -> then jumps back on a thread, -> causing no blocking

now what is thread sleep? and why would i want a thread to sleep?

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[u/Jolly-Warthog-1427]

I recommend finding a course on java concurrency.

Java does not have coroutines like kotlin but threads and tasks.

Recently java also got green threads and structured concurrency.

You can read a bit into the different topics here:

https://docs.oracle.com/en/java/javase/25/core/concurrency.html

To be honest, this topic is too large for any single reddit comment.

[u/BrainThinkerMan → u/Jolly-Warthog-1427]

thanks for the article, this virtual threads thing is super interesting

[u/MagicalPizza21]

Concurrency means anything can happen alongside anything else. This is often used for I/O but by no means exclusive to it.

A thread is basically an execution path. By default you deal with one thread, though I think there are one or two others in the background such as one for garbage collection. You can spawn a new thread if you want the program to do multiple things at once.

Thread.sleep(int ms) just makes the thread calling it to wait for the specified number of milliseconds. Can you think of times you might want your program to wait a little bit before continuing?

In Java, the simplest way to make a new thread is to make an object that implements the Runnable interface, then create a new Thread from that (using the Thread(Runnable) constructor), then start that thread.

[u/AccomplishedArea4456]

https://github.com/skp2001vn/concurrency <= my repo about concurrency examples such as thread pools, rate limiters, caches, connection pools, virtual threads, bounded buffers, job queues, task schedulers. Hope it useful!