Expression

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

Related concepts:  EvaluationValue

Closest Wikipedia entry:  Expression (computer science)

Misconceptions about Expression

51 documented Misconceptions

ArithmeticPlusPrecedes — Java

Addition has higher precedence than string concatenation

AssignCompares — Java

= compares two values

AssignmentNotExpression — Java

An assignment a=b is not an expression

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

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

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

ExpressionsDynamicallyTyped — Java

One has to evaluate an expression to determine its type

LargeIntegerLong — Java

Large integer numbers have type long

LiteralNoExpression — Java

A literal is not an expression

MapToBooleanWithConditionalOperator — Java

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

NoAtomicExpression — Java

Expressions must consist of more than one piece

NoShortCircuit — Java

&& and || always evaluate both operands

ObjectsMustBeNamed — Java

A variable is needed to instantiate an object

OutsideInMethodNesting — Java

Nested method calls are invoked outside in

ParenthesesOnlyIfArgument — Java

() are optional for method calls without arguments

RightToLeftChaining — Java

Chained accesses are invoked from right to left

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

ThisNoExpression — Java

The name this is not an expression

VariablesHoldExpressions — Java

= stores an expression in a variable

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'

ConditionalOperatorNotExpression — JavaScript

The conditional operator is not an expression

IdentifierAsStringInBracketNotation — JavaScript

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

MandatoryAssignment — JavaScript

An expression must be assigned to have a valid statement

NoAtomicExpression — JavaScript

Expressions must consist of more than one piece

NoFunctionCallsChaining — JavaScript

It is not allowed to chain function calls

AssignCompares — Python

= compares two values

CannotChainAttributeAccesses — Python

Attribute accesses cannot be chained together

CannotChainAttributeToObjectInstantiation — Python

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

ComparisonWithBoolLiteral — Python

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

MapToBooleanWithTernaryOperator — Python

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

NoAtomicExpression — Python

Expressions must consist of more than one piece

NoShortCircuit — Python

and/or always evaluate both operands

NoSingleLogicAnd — Python

& is only a bitwise AND

ObjectsMustBeNamed — Python

A variable is needed to instantiate an object

OutsideInFunctionNesting — Python

Nested function calls are invoked outside in

ParenthesesOnlyIfArgument — Python

() are optional for function calls without arguments

PlusConcatenatesNumbers — Python

The plus operator can concatenate strings and numbers

RightToLeftChaining — Python

Chained accesses are invoked from right to left

SelfNoExpression — Python

The name self is not an expression

StringLiteralNoObject — Python

One needs to call str to instantiate a str object from a string literal

VariablesHoldExpressions — Python

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

CompareBooleanToConstant — Scratch

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

EqualityOperatorComparesListIdentities — Scratch

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

ExpressionAssigns — Scratch

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