The Java Language Specification, Third Edition

CHAPTER15
Expressions
When you can measure what you are speaking about,
and express it in numbers, you know something about it;
but when you cannot measure it, when you cannot express it in numbers,
your knowledge of it is of a meager and unsatisfactory kind:
it may be the beginning of knowledge, but you have scarcely,
in your thoughts, advanced to the stage of science.
—William Thompson, Lord Kelvin
MUCH of the work in a program is done by evaluating expressions, either for
their side effects, such as assignments to variables, or for their values, which can
be used as arguments or operands in larger expressions, or to affect the execution
sequence in statements, or both.
This chapter specifies the meanings of expressions and the rules for their evaluation.
15.1 Evaluation, Denotation, and Result
DRAFT
When an expression in a program is evaluated (executed), the result denotes one
of three things:
• A variable (§4.12) (in C, this would be called an lvalue)
• A value (§4.2, §4.3)
• Nothing (the expression is said to be void)
Evaluation of an expression can also produce side effects, because expressions
may contain embedded assignments, increment operators, decrement operators,
and method invocations.
An expression denotes nothing if and only if it is a method invocation
(§15.12) that invokes a method that does not return a value, that is, a method
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