Compile-time and Runtime Constants
Please learn from the following code first
Its outputs is as follows:
Compile-time Constant: A variable use
final modifier, its type is
primitive type or
String, and its value is a
What is constant expression?
Constant Expressions in Oracle
e.g. Constant expressions:
A 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
Casts to primitive types and casts to type String
The unary operators +, -, ~, and ! (but not
The multiplicative operators *, /, and %
The additive operators + and -
The shift operators <<, >>, and >>>
The relational operators <, <=, >, and >= (but not
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.
Qualified names of the form TypeName . Identifier that refer to constant variables.
Constant expressions of type String are always “interned” so as to share unique instances, using the method String.intern.
A constant expression is always treated as FP-strict, even if it occurs in a context where a non-constant expression would not be considered to be FP-strict.
All in all, except for
Runtime constant: A variable use
static modifier, except for compile-time constant.
Compile-time constants’ reference will be replaced with the actual value, like as follows.