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I know this may be basic to many but could somebody explain the difference between compile-time constants and run-time constants. I am guessing final and static variables are comile time variables. Am I right?
This is from the Java Language Specification 15.28.
A compile-time constant expression is an expression denoting a value of primitive type or a String that does not complete abruptly and is composed using only the following:
* Literals of primitive type and literals of type String (�3.10.5) * Casts to primitive types and casts to type String * The unary operators +, -, ~, and ! (but not ++ or --) * The multiplicative operators *, /, and % * The additive operators + and - * The shift operators <<, >>, and >>> * The relational operators <, <=, >, and >= (but not instanceof) * The equality operators == and != * The bitwise and logical operators &, ^, and | * The conditional-and operator && and the conditional-or operator || * The ternary conditional operator ? : * Parenthesized expressions whose contained expression is a constant expression. * Simple names that refer to constant variables (�4.12.4). * Qualified names of the form TypeName . Identifier that refer to constant variables (�4.12.4).
It might make sense for a compile-time constant to be static, but that's not a requirement (except in an interface).
"Constant variable" is defined under JLS - 4.12.4 final Variables: "...a variable, of primitive type or type String, that is final and initialized with a compile-time constant expression (�15.28) a constant variable." The key here is the definition of "compile-time constant expression," which is the section Keith quoted above.
I don't think the term "runtime constant" is formally defined. But I suppose conceptually...
final int i = (int)(Math.random() * 10); [ November 08, 2006: Message edited by: marc weber ]
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