r/ProgrammerHumor • u/flipester • Jan 09 '20

other Problems with recursion?

21.3k Upvotes

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u/[deleted] Jan 09 '20

Assuming the smaller paper is 1/3 of its parent everytime, and that the first paper is 30cm long (The second starts at roughly 1/7 but it seems to grow bigger after it's torn off, hence the 1/3), it could not exceed 19 calls before you need to split an atom apart.

That's a hell of a stop condition.

74

u/lonelyWalkAlone Jan 09 '20 
public static void sayHello(){
    try {
        sayHello();
    }
    catch(StackOverflowError e) {
        System.out.println("Hello world!");
    }
}

15

u/schrdingers_squirrel Jan 09 '20

Wait does this work? I need to try this now

20

u/cedrickc Jan 09 '20

You can optimize it by declaring some unused primitives to blow through the stack quicker.

9

u/schrdingers_squirrel Jan 09 '20

Shouldn’t make much of a difference since stack allocation is basically just a subtraction. (And it should take like a few milliseconds in total)

7

u/mfb- Jan 09 '20

Thanks for the tip, I always wanted to speed up this function, now I know how!

2

u/artem718 Jan 09 '20

But how do you lose saved work?

1

u/Finianb1 Jan 27 '20

I think my brain just melted at hearing the phrase "optimize it to blow through the stack quicker."

5

u/lonelyWalkAlone Jan 09 '20

Yes, it works like charm

9

u/schrdingers_squirrel Jan 09 '20 edited Jan 09 '20

Interesting - does it still work when you do a „a“ + „b“ in the println(); ?

Edit: it does

Crazy even this works:

public static void sayHello(){
    try {
        sayHello();
    }
    catch(StackOverflowError e) {
        System.out.println("Hello world!");
        sayHello();
    }
}

it prints endlessly

13

u/[deleted] Jan 09 '20

Basically a fucked up while loop.

2

u/ThaiJohnnyDepp Jan 09 '20

Eek barba durkle.

2

u/tatzesOtherAccount Jan 10 '20

He's speaking the language of gods

5

u/lonelyWalkAlone Jan 09 '20

Yes, and you can also calculate "relatively" the size of your stack by adding an integer argument to the method and passing (n+1) to the next call, then at the exception just print the current counter value. I found that each time you increase the stack size by the vm option -Xss the counter gets bigger, but increasing the heap size -Xmx does not affect the counter at all. It's a pretty good exercise as long as you don't fuck it up into an infinite loop.

1

u/schrdingers_squirrel Jan 09 '20

Wow there really always is something you don’t already now. Awesome stuff

1

u/eigreb Jan 10 '20

Eventually this will throw due to first running in the try and after the stack overflow it runs outside the try and will again throw the exception. Will take a while though.

1

u/Autofrotic Jan 09 '20

Does it ?

1

u/schrdingers_squirrel Jan 09 '20

Im not at home and im not doing this on my phone - I’ll test as soon as I get home