Type

A type is a set of values supporting a certain set of operations.

Related concepts:  ValueClass

Closest Wikipedia entry:  Type system — In computer programming, a type system is a logical system comprising a set of rules that assigns a property called a type (for example, integer, floating point, string) to every term (a word, phrase, or other set of symbols). Usually the terms are various language constructs of a computer program, such as variables, expressions, functions, or modules. A type system dictates the operations that can be performed on a term.

Misconceptions about Type

38 documented Misconceptions

ArrayElementTypeRepeats — Java

The type of a multi-dimensional array is written as T[] T[] T[]

ArrayElementsUntyped — Java

Elements of arrays are untyped

ArrayLengthPartOfType — Java

The length of an array is part of its type

ArrayRankNotPartOfType — Java

The rank of an array is not part of its type

CharNotNumeric — Java

Char is not a numeric type

CharType — JavaScript

A single character is of type char

ClassDefinesType — JavaScript

The type of an object is equivalent to the type defined by its class definition

CompositeExpressionsUntyped — Java

Expressions that consist of multiple parts have no type

EqualityOperatorComparesOnlyTypes — JavaScript

The equality operator '==' compares only the types of the operands

EqualityOperatorComparesOnlyTypes — Scratch

() = () compares only the types of its operands

ExpressionsDynamicallyTyped — Java

One has to evaluate an expression to determine its type

IntegerDivisionToRational — Java

Dividing two integers can produce a rational number

LargeIntegerLong — Java

Large integer numbers have type long

ListsHomogeneous — Scratch

All items in a list must have the same type

MethodWithoutReturnType — Java

A method declaration does not need to include a return type

NamedTypeParameter — Java

To instantiate a generic type, one needs to specify type parameter names as well as types

NoCastIfSameSize — Java

If a variable is at least as big (bit-width) as a value, then no cast is needed to a assign the value to the variable

NoFloatLiterals — Java

There are no float literals

NoImplicitWidening — Java

Smaller types are never automatically converted into bigger ones without an explicit cast

NoLongLiterals — Java

There are no long literals

NullAndUndefinedAreTheSame — JavaScript

The values null and undefined are the same

NumericToBooleanCoercion — Java

Numeric types can be coerced to boolean

PrimitiveTypeParameter — Java

Type parameters of generic types can be assigned primitive types

PrimitiveVariablesDynamicallyTyped — Java

The type of a primitive variable depends on its value

RecursiveMethodImpliesRecursiveType — Java

A class with a recursive method represents part of a recursive data structure

ReferenceLabeledWithDynamicType — Java

In stack and heap diagrams, reference variables are labeled with the types of the objects they refer to

ReferenceToBooleanCoercion — Java

Every reference type can be coerced to boolean

ReferenceToIntegerConversion — Java

One can cast between references and ints

StaticCallPolymorphic — Java

A static method call is dispatched polymorphically at runtime based on the argument types

SubtypeCompatibleWithSupertype — Java

A variable of a subtype can reference an object of a supertype

SupertypeIncompatibleWithSubtype — Java

A variable of a supertype cannot reference an object of a subtype

TargetTyping — Java

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

TypeofArrayIsArray — JavaScript

The typeof operator applied on an array returns 'array'

TypeofNullIsNull — JavaScript

The value null is of type 'null'

UntypedVariables — Java

Variable declarations don't need a type

UseOfSelfTypeImpliesRecursiveType — Java

If a class has a method that has a local variable, parameter, or return value with the class as its type, the class is a recursive type

VoidMethodNotRecursive — Java

A method with void return type can't be recursive

VoidMethodReturnsValue — Java

A method with void return type can return a value