Cours 10 : Type générique
Java depuis la version 1.0. - permet d'écrire du code plus sûr et plus facile à lire qu'un code parsemé de variables Object
Programmation Objet Java–Classes Génériques
Classe générique (Generic class) : une classe dont la définition est paramétrée avec un ou plusieurs types « variables ». class Stack <T> { void push(T o){.
Generics (in Java)
5. Recently : push for simplifying/eliminating wildcards!!! Page 4. 1 A Generic Swap: in different languages template <class T>.
Types paramétrés
Generics de Java. ? Pour : – Le code du generic est vérifié à compile time lors de sa définition. – Le compilateur transforme le code générique en code.
A Generic Type-and-Effect System
24 janv. 2009 Effect systems have recently been used to enforce a locking discipline to prevent race conditions in. Java (Flanagan and Freund 2000; Abadi et ...
Generics in the Java Programming Language
16 févr. 2004 In the introduction we saw invocations of the generic type declaration List
Safe instantiation in Generic Java
The Safe Instantiation Principle: Instantiating a generic class with types that meet the declared constraints on the parameters should not generate any type
Global Type Inference for Featherweight Generic Java
We study global type inference for Featherweight Generic Java (FGJ) a functional Java core language. Given generic class headers and field specifications
Efficient Implementation of Run-time Generic Types for Java
Java which does not support run-time generic types. Our implementation of. NextGen consists of a compiler extending the GJ compiler and a special class.
Efficient Implementation of Run-time Generic Types for Java
Java which does not support run-time generic types. Our implementation of. NextGen consists of a compiler extending the GJ compiler and a special class.
[PDF] Java Generics
You can define your own class as a generic class The class definition code is parameterized by a type typically called This is more or less what
[PDF] Generics in the Java Programming Language - Oracle
5 juil 2004 · A generic type declaration is compiled once and for all and turned into a single class file just like an ordinary class or interface
[PDF] Java Generics
Java generics are realized by mapping parametric genericity to inheritance genericity – The compiler removes all type parameters / arguments
[PDF] Java - Generics - Tutorialspoint
A type parameter also known as a type variable is an identifier that specifies a generic type name The type parameters can be used to declare the return type
[PDF] JAVA GENERICS - Cornell Computer Science
Early versions of Java lacked generics Proposals for adding Generics to Java Java's type system allows the analogous rule for arrays:
[PDF] Generics in Java
Generic types are erased by type erasure in the compiled program ? At runtime there exist only one http://java sun com/j2se/1 5/ pdf /generics-tutorial pdf
[PDF] Generics (in Java)
Java generics simply provide compile-time type safety and eliminate the need for casts Generics use a technique known as type erasure as described above 2013
[PDF] Java et Généricité - FR
One of the new features of Java 1 5 are the Generics They allow us to abstract over types and help us to write type safe code The generics are in some aspects
[PDF] Generics in Java - BVRIT Hyderabad
The Java Generics programming is introduced in J2SE 5 to deal with type-safe objects It makes the code stable by detecting the bugs at compile time Before
[PDF] Java Generics - Department of Computer Sciences
Generics class can be instantiated only with classes (not primitive types) However autoboxing and unboxing of primitive types make generics act as if they
Introduced in JDK1.5 Classes, Class methods and Interfaces can be generic Generic types are erased by type erasure in the compiled program At runtime there exist only one implementation of the generic code(class,method,interface) Multiple generic parameters Wildcard generics arguments. Bounding generic parameter both upper and lower Default upper bound is Object. Type correctness is checked at compile time, using the upper bound of the generic parameters
public class HolderHolder hi=new Holder(45);
System.out.println(h.getValue());
System.out.println(hi.getValue());
System.out.println(h.getClass());
System.out.println(hi.getClass());
Output
Generic parameters come after the name of the class The class of the variables h and hi are Holder. Generic Classes don't infer types from constructor arguments. Have to specify the type two places The code of the class must valid for the bound of the generic parameterUsageString
45class Holder class Holder public class _2Parameters
T value1;
P value2;
public _2Parameters(T a_value,P a_value2){ value1=a_value; value2=a_value2; } public T first(){ return value1; public P second(){ return value2;}Generic class multiple generic parameters _2Parameters
System.out.println(_2par.first());
System.out.println(_2par.second());
Output
The Generic Parameter list is comma separated.Usagetest 45class Throwable_1
}Generic classes may not be direct or indirect subclass of ThrowableThrowable_1
OutputUsage The catch mechanism only works with non generic types Exception in thread "main" java.lang.Error: Unresolved compilation problem:
The generic class Main.Throwable_1Output
Generic Paremeters comes after scope but before return value of the method Generic Methods do infer the generic types from passed values.UsageIn Normal Class:45
In Normal Class:String
public class Normal{ publicThe method getValue() is undefined for the type T
at Normal.printValue(Normal.java:6) at Main.main(Main.java:91) The Generic Parameter T is unbounded so it defaults to Object. Object don't have a getValue function It does not matter that we only send objects of Holder to it
Effects of Type Erasure
public class Normal{ public void printHolder(Holder}Generic method Overloading The Generic arguments
System.out.println("In Normal Class:"+a_value.getValue()+" Its a string"); } public int printHolder(Holder
OutputUsageIn Normal Class:450
In Normal Class:String Its a string
The correct method gets called. Has to return a value public class Normal{ public void printHolder(HolderSystem.out.println("In Normal Class:"+a_value.getValue()+" Its a string"); } public void printHolder(Holder
OutputUsageIn Normal Class:450
In Normal Class:String Its a string
The correct method gets called. Has to send in a dummy valuepublic class Specialisation
StatTest s2=new StatTest();
System.out.println(s1.getId());
System.out.println(s2.getId());
OutputUsage2
2 The field id are static and are therefore shared by all instances of StatTest. The Generics are type erased so eventhough the generic arguments are different the end type is the same StatTest
Bounding
Example Class Hirachy.
privateSquare square=new Square();
TestExtends(_2d);
TestExtends(square);
//TestExtends(geo);Geometry is not a subclass of _2DOutputUsageclass _2D
class Square T extends ClassType, allows all classes that are subclasses and the class itself.private
OutputUsageclass Cube
class Square T extends ClassType & InterfaceType, allows all subclasses of ClassType and the ClassType itself that are Subclass or the class it self that of a class that implements InterfaceType. More interfaces can be specified seperated by &
private
OutputUsage T extends InterfaceType & InterfaceType2, T is a class subclass of a class that implements InterfaceType1 and InterfaceType2class Cube
class SquareGeneric arguments
TypeArguments: < ActualTypeArgumentList > ActualTypeArgumentList: ActualTypeArgument ActualTypeArgumentList , ActualTypeArgument ActualTypeArgument: ReferenceType Wildcard Wildcard: ? WildcardBoundsOpt WildcardBounds: extends ReferenceType super ReferenceType Generic Arguments Specification
public void DistinctGenericArgument(Holder
OutputUsageclass Geometry
The type of the given variable must be the exact same as the argument type.public void WildChild(Holder extends Geometry> value){ System.out.println(value.getValue().getClass()); }Childed wild card WildChild(new Holder
OutputUsageclass Geometry
class Cube class Square The generic type of the given variable must be a child of the generic argument type or it.public void WildParent(Holder super Square> value){ System.out.println(value.getValue().getClass()); }Parent wild card WildParent(new Holder
public class GeoHolder
OutputUsageclass Geometryclass _2Dclass Square
To upper bound a wild card the generic parameter can define the upper boundpublic class Write
OutputUsage Can't write to values affected by the wildcard.Exception in thread "main" java.lang.Error: Unresolved compilation problem: The method setName(capture#8-of ? extends String) in the type Main.Write
}Generic arguments may not be primitive typesHolder
The Java Language Specification, Third Editionhttp://java.sun.com/docs/books/jls/third_edition/html/j3TOC.htmlGenerics in the Java Programming Languagehttp://java.sun.com/j2se/1.5/pdf/generics-tutorial.pdf
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