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Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

B

bounded wildcard

Example:

public class Collections {
  public static <T> v oid copy 
  ( List<? super T> dest, List<? extends T> src) {  // bounded wildcard parameterized types
      for (int i=0; i<src.size(); i++)
        dest.set(i,src.get(i));
  }
}

bridge method

A synthetic method that the compiler generates in the course of type erasure .  It is sometimes needed when a type extends or implements a parameterized class or interface.

Example (before type erasure):

interface Comparable <A> {
  public int compareTo( A that);
}
final class NumericValue implements Comparable <NumericValue> {
  ...
  public  int compareTo( NumericValue t hat) { return this.value - that.value; }
}

Example (after type erasure):

interface Comparable {
  public int compareTo( Object that);
}
final class NumericValue implements Comparable {
  ...
  public  int compareTo( NumericValue t hat)   { return this.value - that.value; }
  public  int compareTo(Object that) { return this.compareTo((NumericValue)that);  }   // bridge method
}

see also:  TechnicalDetails.FAQ102

C

checked collection

class literal

A literal of type Class . A class literal is an expression consisting of the name of a class, interface, array, or primitive type, or the pseudo-type void , followed by the suffix " .class ".

Example:

if (s.getClass() == String.class ) ...

code sharing  

code specialization  

A translation technique for generics where the compiler generates code for only one representation of a generic type or method and maps all the instantiations of the generic type or method to the unique representation, performing type checks and type conversions where needed.  

see also: TechnicalDetails.FAQ100

concrete instantiation

concrete parameterized type  

An instantiation of a  generic type where all  type arguments are concrete types rather than  wildcards . 

D

E

explicit type argument specification

Providing a type argument list when a generic method is invoked rather than relying on type inference .

Example:

F

G

A class or interface with one or more type parameters .

Examples:

class List<E> { ... }
interface Comparable<T> { ... }
interface Map<K,V> { ... }

Synonyms:   parameterized type

Most authors use the term  parameterized type as a synonym for an instantiation or an invocation of a generic type.  Some (few) authors use the term  parameterized type as a synonym for  generic type .  

see also:  GenericTypes.FAQ001 , JLS 8.1.2

A method with one or more type parameters .

Examples:

<T> void set(T arg) { ... }
<T> T[] toArray(T[] array) { ... }

see also:  GenericMethods.FAQ001 , JLS 8.4.4

Examples:

see also: 

H

I

A method created from a generic method by providing an actual type argument per formal type parameter . It is the result of either type argument inference or explicit type argument specification .

Example:

List<Number> list = new ArrayList<Number>();
Object[] numbers2 = list.toArray(new Long[0]);          // calls method <Long>toArray
Object[] numbers1 = list.<Number>toArray(new Long[0]);  // calls method <Number>toArray

In line 1 an instantiated method with the signature Long[] toArray(Long[]) is created from the generic method <T> T[] toArray(T[] a) by replacing the formal type parameter T with the actual type argument Long .
In line 2 an  instantiated method with the signature Number[] toArray(Number[]) is created from the  generic method <T> T[] toArray(T[] a) by replacing the formal type parameter T with the actual type argument Number .

see also:  TechnicalDetails.FAQ401 ,  TechnicalDetails.FAQ402

A type created from a generic type by providing an actual type argument per formal type parameter .

Examples:

List<String>                                    (created from the generic type List<E> )
Map<String,Date>                            (created from the generic type Map<K,V> )

Synonyms: instantiation , parameterized type , invocation

Most authors use the terms instantiation (short for: instantiated type ) or  parameterized type . The JLS and  other documents by Sun Microsystems use the terms invocation and parameterized type . 

see also:  GenericTypes.FAQ001 , JLS 8.1.2

A type created from a generic type by providing an actual type argument per formal type parameter .  Used to denote both the process of creating a type from a  generic type or method as well as the result of that process.

Examples:

List<String>            (created from the generic type List<E> )
Map<String,Date>    (created from the generic type Map<K,V> )

Synonyms:  parameterized type , instantiation , instantiated type

The JLS and  other documents by Sun Microsystems use the term  invocation for the process and result of creating a type from a generic type by replacing formal type parameters by actual type arguments. The JLS uses the term  parameterized type as a synonym for the resulting type.  Most authors use the term instantiation .   This FAQ prefers the terms  parameterized type and  instantiation  over  invocation .

Other Meanings:

The term invocation is also used in conjunction with methods and means calling a method .

see also:  GenericTypes.FAQ001 , JLS 8.1.2

instantiation

A type created from a generic type or a generic method by providing an actual type argument per formal type parameter . Used to denote both the process of creating a type or method from a  generic type or method as well as the result of that process.

Examples:

List<String>                                    (created from the generic type List<E> )
Map<String,Date>                            (created from the generic type Map<K,V> )
Collections.<Number>toArray     (created from the generic method <T> T[] Collections.toArray(T[]) )

Synonyms: parameterized type , invocation

Most authors use the term instantiation . The JLS and  other documents by Sun Microsystems use the term  invocation for the process and result of creating a type from a generic type by replacing formal type parameters by actual type arguments. The JLS uses the term  parameterized type as a synonym for the resulting type. The JLS has no term for the result of creating a method from a generic method.

Other Meanings:

The term instantiation is also used to denote the creation of an instance (or: object) of a type.

see also:  GenericTypes.FAQ001 , JLS 8.1.2

J

K

L

lower bound

see:  lower wildcard bound

lower wildcard bound

A reference type that is used to further describe a  wildcard ; it denotes the family of types that are supertypes of the lower bound.

Example:

M

N

O

P

A type created from a generic type by providing an actual type argument per formal type parameter .

Examples:

List<String>            (created from the generic type List<E> )
Map<String,Date>    (created from the generic type Map<K,V> )

Synonyms: invocation , instantiation ,  instantiated type

One of the most blurred terms in the area of generics. The JLS uses the term parameterized type for the result of replacing formal type parameters by actual type arguments; it is a synonym for an invocation of a generic type.
Other authors use the term  instantiation or  instantiated type e instead.  Few authors equate  parameterized type with  generic type .
This FAQ favors the terms  parameterized type and  instantiation of a generic type.

see also:  GenericTypes.FAQ001 , JLS 8.1.2

Q

R

A type created from a generic type by omitting the type arguments.

Examples:

List (created from the generic type List<E> )
Map  (created from the generic type Map <K,V> )

see also:  GenericTypes.FAQ201 , JLS 4.8

see also: T TechnicalDetails.FAQ101A TechnicalDetails.FAQ101A TechnicalDetails.FAQ101A TechnicalDetails.FAQ101A echnicalDetails.FAQ101A  

A type whose type information is fully available at runtime, that is, a type that does not lose information in the course of  type erasure .

Examples:

int
Number
List<?>
List
Pair<?,?>[]

but not:

List<String>
List<? extends Number>

see also: TechnicalDetails.FAQ106 , JLS 4.7  

S

A standard annotation that suppresses warnings for the annotated part of the program.

Example:

@SuppressWarnings(value={"unchecked","deprecation"})
public static void someMethod() {
  ...
  TreeSet set = new TreeSet();
  set.add(new Date(104,8,11));     // unchecked and deprecation warning suppressed
  ...
}

see also: TechnicalDetails.FAQ004 , JLS 9.6.1.5

T

A reference type or a  wildcard that is used for instantiation /  i nvocation of a generic type or a reference type used for  instantiation /  i nvocation of a generic method .  

Example:

List< ? > list = new LinkedList< String >;

see also: TypeArguments.FAQ001 , JLS 4.5.1

The automatic deduction of the type arguments of a generic method .

Example:

class Collections {
  public static <A extends Comparable<? super A>> A max (Collection<A> xs) { ... }
}

LinkedList<Long> list = new LinkedList<Long>();
Long y = Collections.max(list);  // 1

In line 1 the compiler infers from the method argument's type that the type argument must be A := Long .

see also: TechnicalDetails.html#FAQ401 , JLS 15.12.2.7

The process that maps generic type s and  generic methods and their instantiations / invocations  to their unique byte code representation by eliding type parameters and type arguments .

Example:

before type erasure:  public static <A extends Comparable<? super A>> A max (Collection <A> xs) { ... }

after type erasure:     public static Comparable max (Collection xs) { ... }

see also: TechnicalDetails.FAQ101 , JLS 4.6

A place holder for a type argument . Each type parameter is replaced by a type argument when a  generic type or generic method is  instantiated / invoked .

Example:

interface Comparable <E>   {
  int compareTo( E other);
}

Synonyms:  type variable

The Language Specification uses the terms  type parameter and  type variable as synonyms. Other authors sometimes use the term  generic parameter as a synonym for  type parameter .

see also: TypeParameters.FAQ001 , JLS 4.4

A reference type that is used to further describe a type parameter .  It restricts the set of types that can be used as type arguments and gives access to the non-static methods that it defines.

Examples:

class Enum<E extends Enum<E> > { ... }
<T extends Comparable<? super T> > void sort(List<T> list) { ... }

see also: TypeParameters.FAQ101 , JLS 4.4

A program is considered type-safe if the entire compiles without errors and warnings and does not raise any unexpected ClassCastExceptions at runtime.

see also: Fundamentals.FAQ004

A place holder for a type argument . Each type parameter is replaced by a type argument when a parameterized type or an instantiated method are created.

Example:

interface Comparable <E>   {
  int compareTo( E other);
}

Synonym to type parameter

The Language Specification uses the terms  type parameter and  type variable as synonyms.

see also: TypeParameters.FAQ001 , JLS 4.4

U

unchecked warning

upper bound

see: upper wildcard bound

upper wildcard bound

A reference type that is used to further describe a  wildcard ; it denotes the family of types that are subtypes of the upper bound.

Examples:

V

W

wildcard bound

An anonymous type variable that represents the particular unknown type that the wildcard stands for.  The compiler uses the capture internally for evaluation of expressions and the term "capture of ?" occasionally shows up in error message.

see also:  TechnicalDetails.FAQ501

wildcard instantiation

wildcard parameterized type

see also:  GenericTypes.FAQ301 , JLS 4.5.1

X

Y

Z

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