Java Reference
In-Depth Information
Empty: true
Full: false
Adding A
Adding B
Adding C
Adding D
Adding E
Empty: false
Full: true
Removing A
Empty: false
Full: false
Adding F
Removing B
Removing C
Removing D
Removing E
Removing F
Empty: true
Full: false
Type Parameter Bounds
List<E>
's
E
typeparameterand
Map<K, V>
's
K
and
V
typeparametersareexamples
of
unbounded type parameters
.Youcanpassanyactualtypeargumenttoanunbounded
type parameter.
It is sometimes necessary to restrict the kinds of actual type arguments that can be
passed to a type parameter. For example, you might want to declare a class whose in-
stancescanonlystoreinstancesofclassesthatsubclassanabstract
Shape
class(such
as
Circle
and
Rectangle
).
Torestrictactualtypearguments,youcanspecifyan
upper bound
,atypethatserves
as an upper limit on the types that can be chosen as actual type arguments. The upper
bound is specified via reserved word
extends
followed by a type name.
Forexample,
ShapesList<E extends Shape>
identifies
Shape
asanupper
bound. You can specify
ShapesList<Circle>
,
ShapesList<Rectangle>
,
and even
ShapesList<Shape>
, but not
ShapesList<String>
because
String
is not a subclass of
Shape
.
