Singleton vs "static" Classes

[glass wigeon]

Why would I use a Singleton instead of a simple:
1. final
2. private constructor
3. static methods
Class?

I've heard that "static classes" cannot implement interfaces, but Singletons can... I don't know the language the article was talking about, but, in my code (Java), I can easily implement any interface and restrict acess directly into this class.

Here is an example of my code:

public final class CsvRandom {
    private CsvRandom(){}
    public static String getRandomValue(@NotNull String path) throws IOException, IllegalArgumentException { 
        ... 
    }
}

[brave star]

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[warm turret]

why would i use a singleton
u don't. singletons are considered an anti pattern and pretty much the whole community aligns on that - which is quite rare

the motivation for singletons usually stems from people being too lazy to specifiy dependencies properly and passing then around through a possibly long chain of objects

they abuse them as a tool for easy public access from anywhere

eventhough that's not actually what they are supposed to be used for to begin with

but thats how people use them and why they create them

that comes as a high cost though and usually it hits u back hard quite soon

and then people regret their choice

the proper alternative that fixes the same problems, without having am the downsides, is dependency injection

an idea that is very prominent and fleshed out in most frameworks, such as spring

[glass wigeon]

Omg, didn't know it is an anti-pattern

At my university, this "pattern" is very common to be taught

[glass wigeon]

Just to know:

But is my analogy correct? Would it be an alternative to Singletons?

Or even this is not used

[warm turret]

its a common pattern and probably the most prominent pattern in interviews when they ask u whether u know any antipatterns lol

[warm turret]

i dont quite get ur example. i neither see an interface, nor an implementation or a "static class" (assuming u meant nested class)

u also didn't restrict anything in ur example

the point of a singleton is to ensure that only a single instance of a class can exist, ever

people abuse it for other things, but thats what a singleton is meant for

that being said, it's not simple to create a true singleton. the only correct implementation is the enum-pattern, which is very rarely seen

[glass wigeon]

I mean, my point was:

Singleton restricts access to the only instance of some class.

So, it is kinda the same as declaring a class with static methods and acessing them directly. Since I have just one Singleton class to access the methods, I should access them directly into the class, instead of making this anti-pattern

I hope I've expressed myself well

I'm still learning

[warm turret]

ur talking about an utility class. a class with only static methods that can't be instantiated

like Math

[glass wigeon]

Yes

[warm turret]

but a singleton, being an actual instance, can have state

i. e. fields

which ur thing can't

[glass wigeon]

I mean, if it was possible, I could create a Singleton of Math class

But the only way is to access the things directly inside the Math class

[warm turret]

sure. but math has no state

there are no fields in it

a singleton can have state

[glass wigeon]

Doesn't it have like PI, e? Aren't that fields?

[warm turret]

no. those are constants

[glass wigeon]

Oh, now I think it makes sense

You're talking about mutability, right?

[warm turret]

point is, u could create a BankAccount singleton and it could have ur amount as a field

[glass wigeon]

Singletons can Have

[warm turret]

yes

also, the users of the singleton don't necessarily know that they are dealing with a singleton, as the interface looks like a regular object to them

[glass wigeon]

Uh But couldn't I go to the class with static methods and those kind of things and change those things there?

[warm turret]

with static fields? u could

[glass wigeon]

Instead of changing singleton's states

[glass wigeon]

Yes

[warm turret]

but what if u want to extend a class and implement 2 interfaces

[glass wigeon]

As Singleton only has one instance, I see no diference between that and static fields beeing changed

[warm turret]

i. e. u need to make an object

if ur forced to make an object bc u want to extend a class and implement a few interfaces, u have no choice

[glass wigeon]

Well, I could do it here, coudn't I?

public final class CsvRandom extends X implements Y{
    private CsvRandom(){}

[warm turret]

no

[glass wigeon]

[warm turret]

static methods are not part of inheritance or interfaces

if u want to implement an interface CanEat, u must implement it's non static eat() method

[glass wigeon]

Ohhh

Ohhh ok

Now it makes sense

[warm turret]

anyways, the part that's flawed is: why would u want to ensure that only a single instance can exist

singletons ensure that u can't create 2 instances of them, or 0

its always 1

and that's kinda flawed

there's no reason to enforce that

and if u do, it usually hits u hard a week later

[glass wigeon]

Got it

✅

Can I save this? If I close will this be deleted?

[warm turret]

threads are never deleted

and u can use /bookmark to find it easily again

[glass wigeon]

Okay

Thanks, helped a lod

10/10

Legend

Bye, thanks

/help-thread close