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 — Java

Addition has higher precedence than string concatenation

ArrowFunctionNoImpliedReturn — JavaScript

Even when an arrow function consists just of an expression, the return keyword must be explicitly written

ArrowFunctionRequiresFunctionKeyword — JavaScript

Arrow functions also require the keyword 'function'

AssignCompares — Java

= compares two values

AssignCompares — Python

= compares two values

AssignmentNotExpression — Java

An assignment a=b is not an expression

CannotChainAttributeToObjectInstantiation — Python

Method calls, and attribute accesses in general, cannot be chained to a constructor invocation.

CannotChainMemberAccesses — Java

Member accesses cannot be chained together

CannotChainMemberToConstructor — Java

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

ChainedMethodsNotCalledFromOutside — Java

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

CompareBooleanToConstant — Scratch

To test whether an expression evaluates to true or false, one must compare it to a constant

ComparisonWithBoolLiteral — Python

To test whether an expression is True or False, one must compare it to True or to False

ComparisonWithBooleanLiteral — Java

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

CompositeExpressionsUntyped — Java

Expressions that consist of multiple parts have no type

ConditionalOperatorNotExpression — JavaScript

The conditional operator is not an expression

EqualityOperatorComparesListIdentities — Scratch

(list a) = (list b) compares the identities of list a and list b

EqualityOperatorComparesObjectsValues — Java

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

EqualsComparesReferences — Java

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

ExpressionAssigns — Java

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

ExpressionAssigns — Scratch

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

ExpressionsDynamicallyTyped — Java

One has to evaluate an expression to determine its type

IdentifierAsStringInBracketNotation — JavaScript

An identifier used to access a property with the bracket notation is treated as a string

InlineCallInExpressionTree — Java

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

InlineVariableInExpressionTree — Java

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

LargeIntegerLong — Java

Large integer numbers have type long

LiteralNoExpression — Java

A literal is not an expression

MandatoryAssignment — JavaScript

An expression must be assigned to have a valid statement

MapToBooleanWithConditionalOperator — Java

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

MapToBooleanWithTernaryOperator — Python

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

NoAtomicExpression — Java

Expressions must consist of more than one piece

NoAtomicExpression — JavaScript

Expressions must consist of more than one piece

NoAtomicExpression — Python

Expressions must consist of more than one piece

NoFunctionCallsChaining — JavaScript

It is not allowed to chain function calls

NoShortCircuit — Java

&& and || always evaluate both operands

NoShortCircuit — Python

and/or always evaluate both operands

ObjectsMustBeNamed — Java

A variable is needed to instantiate an object

ObjectsMustBeNamed — Python

A variable is needed to instantiate an object

OutsideInFunctionNesting — Python

Nested function calls are invoked outside in

OutsideInMethodNesting — Java

Nested method calls are invoked outside in

ParenthesesOnlyIfArgument — Java

() are optional for method calls without arguments

ParenthesesOnlyIfArgument — Python

() are optional for function calls without arguments

PlusConcatenatesNumbers — Python

The plus operator can concatenate strings and numbers

RightToLeftChaining — Java

Chained accesses are invoked from right to left

RightToLeftChaining — Python

Chained accesses are invoked from right to left

SelfNoExpression — Python

The name self is not an expression

StringPlusStringifiesExpression — Java

String concatenation stringifies non-String operand expressions

TargetTyping — Java

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

ThisChildInCallExpression — Java

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

ThisNoExpression — Java

The name this is not an expression

VariablesHoldExpressions — Java

= stores an expression in a variable

VariablesHoldExpressions — Python

= stores an expression: it stores a reference to the expression in a variable