Expression

An expression is a piece of source code that produces a value at runtime.

Related concepts:  EvaluationValue

Closest Wikipedia entry:  Expression (computer science) — In computer science, an expression is a syntactic entity in a programming language that may be evaluated to determine its value. It is a combination of one or more constants, variables, functions, and operators that the programming language interprets (according to its particular rules of precedence and of association) and computes to produce ("to return", in a stateful environment) another value. This process, for mathematical expressions, is called evaluation.

Misconceptions about Expression

51 documented Misconceptions

ArithmeticPlusPrecedes

Addition has higher precedence than string concatenation

AssignCompares

= compares two values

AssignmentNotExpression

An assignment a=b is not an expression

CannotChainMemberAccesses

Member accesses cannot be chained together

CannotChainMemberToConstructor

Method calls or field accesses cannot be chained to a constructor invocation

ChainedMethodsNotCalledFromOutside

Chained methods are all called on the object at the beginning of the chain

ComparisonWithBooleanLiteral

To test whether an expression is true or false, one must compare it to true or to false

CompositeExpressionsUntyped

Expressions that consist of multiple parts have no type

EqualityOperatorComparesObjectsValues

o==p compares the objects referred to by variables o and p

EqualsComparesReferences

o.equals(p) compares the references stored in the variables o and p

ExpressionAssigns

An expression that reads a variable also updates its value after the evaluation

ExpressionsDynamicallyTyped

One has to evaluate an expression to determine its type

InlineCallInExpressionTree

The expression tree of an expression involving a call inlines the call's computation of the returned value

InlineVariableInExpressionTree

The expression tree of an expression involving a variable inlines the variable's definition

LargeIntegerLong

Large integer numbers have type long

LiteralNoExpression

A literal is not an expression

MapToBooleanWithConditionalOperator

To map a boolean expression to a boolean, a conditional operator is necessary

NoAtomicExpression

Expressions must consist of more than one piece

NoShortCircuit

&& and || always evaluate both operands

ObjectsMustBeNamed

A variable is needed to instantiate an object

OutsideInMethodNesting

Nested method calls are invoked outside in

ParenthesesOnlyIfArgument

() are optional for method calls without arguments

RightToLeftChaining

Chained accesses are invoked from right to left

StringPlusStringifiesExpression

String concatenation stringifies non-String operand expressions

TargetTyping

The type of a numerical expression depends on the type expected by the surrounding context

ThisChildInCallExpression

Instance method or constructor call nodes in expression trees have a child labeled "this"

ThisNoExpression

The name this is not an expression

VariablesHoldExpressions

= stores an expression in a variable