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Primatives and Literals

 
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What is the difference between primatives and literals. (if that is a fair question) and how are both treated?
 
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Originally posted by Dale DeMott:
What is the difference between primatives and literals. (if that is a fair question) and how are both treated?



My understanding is: literal concept includes primative concept.
 
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primitive data types are non-composite (read: non-Object) data types. int, char, byte, etc. are primitives.
Literals, on the other hand, are the opposite of variables. They are values that are specified, well, literally in the code.
example:

in this example 1, 'A', 15L, and "Hello, World!" are literals. aValue, aChar, aLong, and aString are variables.
1, 'A', 15L, anInt, aChar, and aLong are primitives. "Hello, World!" is a literal that is an Object; Strings are the only objects that can be literals (This was done becuase Strings are such commonly used critters).
 
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From the JLS :
A literal is the source code representation of a value of a primitive type (�4.2), the String type (�4.3.3), or the null type (�4.1):
A primitive is one of boolean, byte, short, char, int, long, float, double.
What do you mean by "how are they treated"? treated in what respect?

Don Liu:

My understanding is: literal concept includes primative concept.
 
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hi Joel and Dale
According to Don said

My understanding is: literal concept includes primative concept.


The statement is true.
And some special case occur in primative data type such as character array char[]-->string which use the object concept although it is primative data type.
So in the Set theory
Primative data type is subset of literal
I hope that I can answer your question

 
Dale DeMott
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Thanks for your answers. Makes things much clearer.
 
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Neither primitives not literals are subsets or supersets of each other. Examples:

Primitive literals:
1, 'a', false

Literal but not primitive:
"", "a", "This is a string literal", Object.class, ArrayList.class, int.class, int[].class

Primitive but not literal:
Any variable with primitive type, e.g. int

Not pimitive or literal:
Any variable with reference type, e.g. String, ArrayList, Object
 
Dale DeMott
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Yes. I do realize this. After someone stated that they are values and not variables, it made everything quite clear.
 
John Lee
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Dale:
I forget to bring all my SCJP books with me. The first thing I would like to do is check all the definetions. I feel this question isn't very fair, Primatives and Literals are not in the same domain. Primatives is opposite to compositive. Literals is something broader. I agree with siu chung man.
HTH.
 
Francis Siu
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hi Jim
Sorry Jim,
I may be misunderstanding some concept in Java


Neither primitives not literals are subsets or supersets of each other. Examples:
Primitive literals:
1, 'a', false

Literal but not primitive:
"", "a", "This is a string literal", Object.class, ArrayList.class, int.class, int[].class

(*) Primitive but not literal:
Any variable with primitive type, e.g. int


I have question in
(*)Primitive but not literal:
Is (primitive type, e.g. int) including in literal?
Because I do not make sure integer primitive data type which is not literal.
thanks
 
Joel McNary
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Say you had:

the anInt is a primitive but is not a literal; it is a variable.
Also, some primitive types do not have literals. (byte and short come to mind). When you say

the 5 is an integer literal which is cast down to a byte.
Thus, not all primitives are literals, and not all literals are primitives.
Hope this clears up any confusion.
 
John Lee
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I just have a small question:
int n = 23 ;
here, 'int', 'n', '=', and '23' are all literals. aren't they?
 
Francis Siu
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oo........
Please forget it, I do not want to discuss this little thing.
A little little definition differ between each other. :roll:
Anyway,thanks
 
John Lee
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I feel I can choose the correct one out of 4 choices in the exam....
 
Joel McNary
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Originally posted by Don Liu:
I just have a small question:
int n = 23 ;
here, 'int', 'n', '=', and '23' are all literals. aren't they?


They are all tokens in the languange, not literals. Only 23 is a literal. (for that matter, ';' is a token, as well)
 
John Lee
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Originally posted by Joel McNary:

They are all tokens in the languange, not literals. Only 23 is a literal. (for that matter, ';' is a token, as well)


i guess i get it.
token is the literals reserved for the system. but isn't it true that token is a subset of literal. if 'int' is not reserved by system, i guess i can use it like '23' or 'moose'? am i right?
 
Jim Yingst
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Urm... I'm not sure what definition of "token" Joel is using. According to the JLS though, literals are a subset of tokens. Everything in a valid .java file is (or is part of) either a comment, a token, or whitespace. (Note that spaces inside comments or String literals are not considered "whitespace" in this context.) Tokens can be identifiers, keywords, literals, separators, or operators - these five groups do not overlap.
if 'int' is not reserved by system, i guess i can use it like '23' or 'moose'? am i right?
int is a keyword, therefore it cannot be used as an identifier. It can't be a literal unless it's enclosed in double quotes (since it's clearly not a numeric, boolean, or class literal).
23 is not a keyword; it can't be an identifier since it doesn't start with a letter; it's a numeric (int) literal.
moose is not a keyword; it can be an identifier; it can't be a literal unless surrounded with double quotes.
To be fair, I don't think it really matters whether you know what the definition of a token is, unless you're writing a compiler. But understanding the differences between identifiers, keywords, literals, separators, and operators is useful.
 
Joel McNary
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Yup, that's the definition of "token" that I was using...
I do have a (small) background in compilers and interpreters, so "token" just rolls off the tounge.
But Jim is (as usual ) right:
int - keyword
n - identifier
= - operator
23 - literal
; - separator
all of which make up the larger "token" categorization.
 
John Lee
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thanks a lot!
 
John Lee
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Originally posted by Jim Yingst:
Urm... I'm not sure what definition of "token" Joel is using. According to the JLS though, literals are a subset of tokens. Everything in a valid .java file is (or is part of) either a comment, a token, or whitespace. (Note that spaces inside comments or String literals are not considered "whitespace" in this context.) Tokens can be identifiers, keywords, literals, separators, or operators - these five groups do not overlap.
if 'int' is not reserved by system, i guess i can use it like '23' or 'moose'? am i right?
int is a keyword, therefore it cannot be used as an identifier. It can't be a literal unless it's enclosed in double quotes (since it's clearly not a numeric, boolean, or class literal).
23 is not a keyword; it can't be an identifier since it doesn't start with a letter; it's a numeric (int) literal.
moose is not a keyword; it can be an identifier; it can't be a literal unless surrounded with double quotes.
To be fair, I don't think it really matters whether you know what the definition of a token is, unless you're writing a compiler. But understanding the differences between identifiers, keywords, literals, separators, and operators is useful.


Thanks for the help! now i have to start all over, again!
 
Jim Yingst
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[Joel]: Yup, that's the definition of "token" that I was using...
Thanks - from your phrasing I thought maybe "token" and "literal" were intended as separate (non-overlapping) categories. I should have known better...
 
John Lee
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Tokens can be identifiers, keywords, literals, separators, or operators - these five groups do not overlap.


cool, i guess this is really what i am looking for. now i am looking forward to scjp 1.4
 
Dale DeMott
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Are we going to need this much detail for any of the tests (tokens etc)
 
John Lee
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Originally posted by Dale DeMott:
Are we going to need this much detail for any of the tests (tokens etc)



By failing to prepare, you are preparing to fail.
Benjamin Franklin (1706 - 1790)


it looks like we have better be prepared!
 
John Lee
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Tokens can be identifiers, keywords, literals, separators, or operators - these five groups do not overlap.


What is the difference between primatives and literals. (if that is a fair question) and how are both treated?


in the original question, it mentioned 'primative', in my previous post, i said this two concepts are from different domains. and i still think so. otherwise, where does 'primative' fit in here?
 
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For these type of questions, it is best to refer to the Java Language Specification. Nothing beats the JLS. Thanks Junilu Lacar for pointing out the relevent sections in the JLS.
 
John Lee
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thanks!
 
John Lee
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Originally posted by Dale DeMott:
What is the difference between primatives and literals. (if that is a fair question) and how are both treated?


i guess this isn't a fair question!
 
Jim Yingst
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It's kind of like "what's the difference between apples and seeds?" You should know what seeds are, and you should know what apples are, but asking what's the "difference" is kind of a silly question. They're very different things. A slightly better question would be what do they have in common? The answer is, not much.
[ May 08, 2003: Message edited by: Jim Yingst ]
 
Dale DeMott
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I agree Jim. After I understood the answer, I realized that they really are quite different.
 
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