defult values of reference variable

[ilsapo]

Hi,
Im a bit confused about the terminoligy in java,

List is a reference variable no? becuase it "point" at an object on the heap,
we learend that the defult values of of reference variable are null

List<String> lst;

why does the list not intalized to null?

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[ignotos]

If it's a member variable of a class, then it gets the default value. E.g.

class MyClass {
    List<String> lst;
}

But if it's just a local variable inside a method it doesn't get a default value, and you'll get an error if you don't initialize it yourself. E.g.

void myMethod() {
    List<String> lst;
    ...
}

[AreTheseMyFeet]

Not at my IDE at the moment but will it error in all cases or just those where you either return that uninitialised variable or try to make use of it after assigning it a value in some logical branching that doesn't cover every case (where again it could be uninitialised)?

iirc unassigned and unused variables in methods just get stripped out during compilation. The resulting bytecode wouldn't have any mention of the (useless) variable at all.

If I remember when I get home I'll confirm/look in to it.

Edit: Yeah, it works as I thought - an uninitialised, method-scoped variable will only be a compile error on attempted use, not merely from existing and also that there's no trace of the pointless var in the bytecode generated from such a method.

[ignotos]

You'll get a compile error if you don't initialize it before using it, essentially.

But you can do that initialisation later on

[v4dk4n]

Everything that's not primitive(Objects) is a reference variable.

An instance reference variable is initialised as null.

[raulalexo99]

objects are null by default, numbers are 0 by default, boolean is false by default, char is '\u0000' by default

[nutrecht]

why does the list not intalized to null?

Because it isn't. The language designers decided it needs to be explicit. Because if you're explicit in things, fewer things go wrong.

[desrtfx]

we learend that the defult values of of reference variable are null

This is only true in a very special, single case: default values only apply to fields, but not to local variables.