Classes concept

Question

I'm having trouble understanding what this means, and how it was coded

Foo number = Foo.NUMBER;

Like, is Foo a class with static things?

(This was posted in an assignment it said "you might want to structure your solution like this")

• Hovercraft Full Of Eels: Like, perhaps. It looks more like code for an enum to me.
• mre: @Hovercraft Full Of Eels, +1 And enums are static by default. :D
• Hovercraft Full Of Eels: @mre: indeed they are! a worthless +1 back atcha! :D
• Hovercraft Full Of Eels: @mre: well, actually all points are worthless, since you can no longer redeem them for beer and pizza. Cheers!
• mre: @Hovercraft Full Of Eels, Mmm...beer. Here, have another +1, cheers! :D

Answer 1

The NUMBER is static (and final) member of Foo class which return Foo object. Take a look at java.awt.Color class.

• bb2: Why isn't there a Foo number = new Foo() or something like that?
• mre: @bb2, Number could be a static instance.
• KV Prajapati: @bb2 With java.awt.Color, you may use new keyword to create an object or you may get instance directly from the defined static FIELDS.
• nicholas.hauschild: This is not necessarily final. If convention is followed it would be. (because constants are in all caps, and must be final to not be reassigned)
• KV Prajapati: @ nicholas.hauschild Yeh agree!

Answer 2

class Foo {
 public static final Foo NUMBER = new Foo();
}
//later... 
Foo number = Foo.NUMBER;

Answer 3

As @Hovercraft pointed out in the comments, it's worth noting that this syntax could (probably?) be referring to enums:

public enum Foo { NUMBER }
Foo number = Foo.NUMBER;

Answer 4

class Foo {
 public static Foo NUMBER = new Foo(); //might be final too...
 public Foo {
 // init Foo instance
 }
}

Here is an example of a class definition that will allow the line of code you posted to compile. Foo is a class with a static member of type Foo identified by the name NUMBER.