generics diamond syntax

[tepid sand]

Hi guys I'm a little confused on generics. I understand what they are for and i see that instead of saying something like Integer thingToPrint you can just say T thingToPrint and T is the generic type. However i don't get how the diamond syntax is used when you put it at the top of a class.

[topaz lichen]

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[tepid sand]

https://youtu.be/K1iu1kXkVoA

Here i was watching a YouTube video and at 13:36 he adds a second generic type, V, but at that point he never had a type V in the top of a class header in diamond syntax, he only did that with T

So I'm confused when to put a generic type in diamond syntax at the top of a class header

[brisk thistle]

he has it in method declaration

private static <T, V> void shout(...)

[tepid sand]

I see that but why doesn't he need to put it on the class header

[brisk thistle]

it's allowed to use generic methods without have whole class as generic

https://docs.oracle.com/javase/tutorial/extra/generics/methods.html

[tepid sand]

I don't understand

I'll check out this website

I think this is too hard for me

They write it so confusing

[brisk thistle]

you can declare generic variable at top of class, but also can declare generic variable at method declaration, so you can use it in scope of that method

[tepid sand]

So if im gonna use the generic everywhere in a class then i write <T> in the class header and then continue calling it T in the rest of the file? But if i want to only use a generic in one method, then i always call it <T> instead of just T whenever i wanna use it?

[shadow aurora]

Hi, generics little bit tricky but its easy to understand simple you just think in one class you have to use every data type but you write constant
example:
class Example {
Integer a;
}
like this but you want to use all datatypes what you do then you have to use generics
class Example<T> {
T a;
}
then when you create object that example class that time you have to pass the type
example :
Example<Integer> object = new Example<>();
Thats it

[tepid sand]

That makes sense

[tepid sand]

But also in the video i linked at the time he puts a generic T but also a V and he never specified a V in the class header

[tepid sand]

Here we have a <T> on the header

But in the video that never happened but it still worked

[shadow aurora]

class Example<T,V> like this ?

[brisk thistle]

class Tests {
  public static <T, V> void doSomething(T t, V v) { ... }
}```it works, because you declared generic variables for that particular method. No need to declare them at top of class.

[shadow aurora]

yeah that also be work

[tepid sand]

I meant like he doesn't do that

Like he might only have class Example <T> but then in a method he'll say T something and V something

[tepid sand]

Is declaring generic variables for a method is that right after it says static

So that's like the same as putting it in the class header except here we put it in just the method?

[shadow aurora]

method level also you can do generics brother

[brisk thistle]

same as, only that visibility scope is different. If you declare for class, so it will be visible in all class, if you declare it at method declaratiion - it will be visible only for that method

[tepid sand]

Is there anything wrong with declaring it in the class and then using that generic type only for one method, even if there are a bunch of other methods that take in some other specific types

So like declare generic in class header and you have 5 methods but only 1 uses generic is there anything wrong with that

[brisk thistle]

nothing wrong, imo

[tepid sand]

Ok thanks

[topaz lichen]

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[tepid sand]

Thanks for all help

[brisk thistle]

👍

[brisk thistle]

Could you close the post please?

[tepid sand]

Sorry didn't notice it didnt close