Confused myself learning Java... please help

[N00Bie]

Hi,
While going through my tutorials I have confused myself in one area.
This part:

Food foodObject = new Food();

The bolded part below is what confuses me now:

[B]Food[/B] foodObject = new Food();

Why do we need to tell java twice that we need to create a new instance of Food?

Why not just:

foodObject = new Food();

?

[Junky]

What you have to realise that the

Food foodObject = new Food();

line of code is doing 2 things. It is declaring a variable and it is initialising the variable. The very first time you use a variable in a program you need to tell the compiler what its type is.

Type variableName;  // perfectly legal
//later
variableName = ....
// or all on one line
Type variableName = ...

What do the ... mean? Well if it was a primitive then you could just hard code a literal value. If it was a reference type (ie object) the you use the new keyword to invoke the constructor. Another possibility is a method call or compund statement such as a mathematical formula.

String stringOne = "hello ";
String stringTwo = "world";
int x;
int y;
int z = 2;
String s;
Foo f;
x = 7;
y = x * z;
s = stringOne + stringTwo;
f = methodThatReturnsAFooObject();

I hope that helps.

[N00Bie]

Thanks! I think I got it thanks to your explanation.
This is the part that really helped:

line of code is doing 2 things...

just to confirm, this:

Food foodObject = new Food();

and this:

Food foodObject;
foodObject = new Food();

Is identical, except that "Food foodObject = new Food();" is doing it more efficiently in one line instead of two.

Yes?

[Junky]

Depends upon what you mean by efficient. When the JVM executes the code I'm sure it makes no difference if it were on one or two. In fact if it were on two lines then it is possible that the compiler will change it to one line.

[N00Bie]

Depends upon what you mean by efficient. When the JVM executes the code I'm sure it makes no difference if it were on one or two. In fact if it were on two lines then it is possible that the compiler will change it to one line.

Sorry, I meant human efficient / easy to read but to the computer/jvm it looks exactly the same as the two line example written above.

[N00Bie]

I think one of the reasons I got so confused was that I tend to think of variables as (I dont know the exact word, but I think its "primitive") either
int
string
double
etc

so getting around the concept of:
make a class Foo
have nothing in that class (no methods, variables)
then make a variable of that class like so "Foo foo;" in class Bar
now what the heck is foo? (I know its a variable of class Foo but in my head my brain is screaming: its not a int, its not a string, its not a double its not a boolean... and class Foo does not contain anything... what type does that fall under? ARRRRGH!!!!!!)

[goldest]

Go through this for more details about variables: Java Variables

Hope that helps,

Goldest

[N00Bie]

Go through this for more details about variables: Java Variables

Hope that helps,

Goldest

Thanks for the link! Will check it out now;)