Angular 2 when to use DI, provider or pure import?

I am little confused when is proper to use what.

1. Define class with static functions, just import and use imported name and then function

Shared class:

export class SomeClass {
static someFunction(){
...
}
}


Class which uses exported class:

import { SomeClass } from './someclassstatic'
...
constructor(){
SomeClass.someFunction()
}


2. Define standard class, then mount via DI

Shared class:

export class SomeClassDI {
public someFunctionDI(){
...
}
}


Class which uses exported class:

import { SomeClassDI } from './someclassdi'
...
constructor(private theclassdi:SomeClassDI){
this.theclassdi.someFunction()
}


3. Define standard class, then mount as provider while bootstraping

Shared class:

export class SomeClassBS {
public someFunctionBS(){
...
}
}


Class that bootstraps Angular2

import { SomeClassBS } from './someclassbs'
...
bootstrap(AppComponent, [SomeClassBS]);


Class which uses exported class:

??? I am not sure what can be the example here.


What is the proper use of the providers?

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