An expression is a rule for computing a value.
An expression consists of one or more operands combined by means of language-defined operators. Operands used in expressions can be one of the following.
A literal value; for example; 1, true, null, "hello" (for more details, see "Literals", later in this section)
A constant value; for example, Red, SecondsInDay (for more details, see "Constants", later in this section)
A property (attribute or reference)
A local variable (for more details, see "Variable Declaration", earlier in this chapter)
A formal parameter (for more details, see "Parameters", earlier in this chapter)
A method call or inheritMethod call
A type (for more details, see "Type Casts", later in this section)
System variables (for more details, see "System Variables", later in this section)
For details about constructing composite expressions with operators, see "Expressions with Operators" and "Operator Precedence", later in this chapter.