Subtyping

A value of a subtype can be substituted for a value of a supertype.

Related concepts:  TypePolymorphismInheritance

Closest Wikipedia entry:  Subtyping — In programming language theory, subtyping (also called subtype polymorphism or inclusion polymorphism) is a form of type polymorphism. A subtype is a datatype that is related to another datatype (the supertype) by some notion of substitutability, meaning that program elements (typically subroutines or functions), written to operate on elements of the supertype, can also operate on elements of the subtype. If S is a subtype of T, the subtyping relation (written as S <: T, S ⊑ T, or S ≤: T ) means that any term of type S can safely be used in any context where a term of type T is expected.

Misconceptions about Subtyping

11 documented Misconceptions

CallNotStaticallyChecked

A method invocation on a reference of a type that does not have that method won't compile

ConcreteClassOnlyImplementClassAbstract

A concrete class only needs to implement those abstract methods it inherits from abstract superclasses

ConcreteClassOnlyImplementDirectAbstract

A concrete class only needs to implement abstract methods declared in its direct supertypes

ConcreteClassOnlyImplementInterfaceAbstract

A concrete class only needs to implement those abstract methods it inherits from interfaces

ExceptionRoot

Exception is the top-most exception class

InterfaceExtendClass

An interface can extend a class

MultipleSuperclasses

A class can have multiple superclasses

RuntimeExceptionChecked

RuntimeExceptions are checked exceptions

StaticDispatch

The method to be called is determined by the static type

SubtypeCompatibleWithSupertype

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

SupertypeIncompatibleWithSubtype

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