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Java Generics Runtime Information


Has to be created as anonymous implementation (new Generic() {};) share|improve this answer edited Nov 30 '15 at 14:16 answered Nov 30 '15 at 11:13 Yaroslav Kovbas 13213 add a comment| This allows us to successfully run the following application:Class genericType = findSuperClassParameterType(new MyStringSubClass(), MyGenericClass.class, 0); assert genericType == String.class; Be however aware thatfindSuperClassParamerterType(new MyGenericClass(), MyGenericClass.class, 0)will throw an exception in this There are a lot of blogs out there about such a type-safe generic DAO pattern and you can even download some code from [...] Rob - Reply June 12, 2009 at It defines one or more type variables that act as parameters. http://analysedesgeeks.com/java-get/java-generics-runtime-type-checking.html

Type[] actualTypeArguments = parameterizedType.getActualTypeArguments(); –Ondrej Bozek Sep 13 at 14:44 add a comment| up vote 11 down vote I dont think you can, Java uses type erasure when compiling so your In this case, the actual the Type object returned by getGenericSuperClass will be a ParameterizedType instance. A bit nicer. –Joeri Hendrickx Aug 1 at 20:04 | show 1 more comment up vote 138 down vote I have seen something like this private Class persistentClass; public Constructor() { class UserExecutor extends AbstractExecutor { @Override public User create(String name) { return new User(name); } // ... } share|improve this answer edited Oct 15 '10 at 12:52 answered Oct 15 '10 http://stackoverflow.com/questions/3403909/get-generic-type-of-class-at-runtime

Java Get Generic Type At Runtime

For all we know, MyGenericInnerClass could be static and define its own generic variable name space. Ray Feb 4 '14 at 0:15 @CodyA.Ray This approach seems to battle type erasure in the most elegant way. These type variables are known as the type parameters of the interface.

Constant c = new Constant(new Integer(0)); Class n = c.getClassType(); returns Integer.class when it should return Number.class. It works, but i didn't like not having an elegant solution either. Output integers in negative order, increase the maximum integer everytime Difference between "raise" and "lift" Find the sum of all numbers below n that are a multiple of some set of Java Gettypeparameters Join them; it only takes a minute: Sign up How to get the generic type at runtime?

Object value = stringList.get(0); And indeed if you try it, you'll find that you can safely pull the 42 value back out as an Object and not have any errors at Java Parameterizedtype super Number> could represent List or List. public abstract class TestGeneric { private final Class aClass; public TestGeneric() { ParameterizedType superclass = (ParameterizedType) getClass() .getGenericSuperclass(); this.aClass = (Class) ((ParameterizedType) superclass) .getActualTypeArguments()[0]; } public static void main(String[] args) throws http://stackoverflow.com/questions/32041109/java-reflection-get-runtime-type-when-using-generics Neither if you are FooUtils and get passed an instance of Foo.

If you allow yourself to think of the class type as "metadata" on the class, that suggests the Java method for encoding metadata in at runtime: annotations. Java Reflection Get Generic Type First define a custom annotation along these lines: import java.lang.annotation.*; @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) public @interface EntityAnnotation { Class entityClass(); } You can then have to add the annotation to your subclass. @EntityAnnotation(entityClass Documentation The Java™ Tutorials Download Ebooks Download JDK Search Java Tutorials Hide TOC Generics (Updated) Why Use Generics? Is Admiral Raddus Related to Admiral Ackbar? "daisy sounded like she had a cold, didn't she?" Since when has Darth Vader had a sense of humor?

Java Parameterizedtype

This type of problem can be avoided by using generics and is the primary motivation for using generics. https://www.javacodegeeks.com/2013/12/advanced-java-generics-retreiving-generic-type-arguments.html Thus we can get rid of all the annoying constructors with Class arguments, and handle determination of the entity type in just one place. Java Get Generic Type At Runtime Type erasure ensures that no new classes are created for parameterized types; consequently, generics incur no runtime overhead. Java Getactualtypearguments share|improve this answer edited Jan 26 at 19:53 jpaugh 2,57111541 answered Aug 4 '10 at 9:22 Joeri Hendrickx 10.2k22545 Seems related: artima.com/weblogs/viewpost.jsp?thread=208860 –ewernli Aug 4 '10 at 10:13 9

I've also added a note clarifying that you must instantiate a subclass (as shown). this content An interface is generic if it declares one or more type variables. As a result, the Java compiler is able to store the information about the generic argument's type String of superclass MyGenericClass in the byte code of its subclass MyStringSubClass. Since the ArrayList.class instance is however shared with other instances which could also be of type ArrayList, this would already require to have two different versions of ArrayList.class. Java Getgenericsuperclass

I found it here, the first time I ever heard about it. There is also the possibility to create generic methods based on given parameters. If a subclass knows the generic arguments of its super class, they can be retreived via reflections. http://analysedesgeeks.com/java-get/java-get-xmx-runtime.html Examples Java Code Geeks is not connected to Oracle Corporation and is not sponsored by Oracle Corporation.

Accessing generic type info at runtime « Ben Thurley - Reply July 18, 2012 at 4:21 pm [...] http://blog.xebia.com/2009/02/07/acessing-generic-types-at-runtime-in-java/ Share this:TwitterFacebookLike this:LikeBe the first to like this. [...] Varun Nagpal - Java Reflect Type There is a rich literature on the subject, and some people are dissatisfied with the current state, some says that actually it's a lure and there is no real need for On the subclass define constructor without parameters and call super(User.class) from there.

extends Number> but not a Class. –Radiodef Apr 11 '15 at 2:30 add a comment| up vote 2 down vote Here is working solution!!! @SuppressWarnings("unchecked") private Class getGenericTypeClass() {     try {         String className

For a more elaborate example, see reference.[4] Here is a small excerpt from the definition of the interfaces List and Iterator in package java.util: public interface List Comments (18) Maarten Winkels - Reply February 7, 2009 at 2:50 pm Hi Arjan, A neat trick indeed. I'm personally more inclined to use that for framework code. Java Type To Class This uses reflection to battle Java's runtime type erasure.

I.e. Has to be extended with typed class (Child extends Generic) OR 2. Then, it adds a String to the ArrayList. check over here Big numbers: Ultrafactorials Using ozone as oxidizer "daisy sounded like she had a cold, didn't she?" How to desiccate your world?

Here is my applaction context:forums.oracle.com/forums/message.jspa?messageID=7006‌003#7006003 –hguser Oct 15 '10 at 12:16 add a comment| up vote 5 down vote I think you should use getActualTypeParameters; as getTypeParameters does not refer to As a completely different alternative, you can make use of polymorphism. From the Oracle Docs: Type Erasure Generics were introduced to the Java language to provide tighter type checks at compile time and to support generic programming. A class is generic if it declares one or more type variables.

Generate bridge methods to preserve polymorphism in extended generic types. The code itself though is just plain nasty, with all the explicit casting and using hardcoded array indexing. In order to get the ParameterizedType you should use getGenericSuperclass first. tutorialspoint.com/… –Lin Yu Cheng Oct 26 at 0:28 add a comment| Your Answer draft saved draft discarded Sign up or log in Sign up using Google Sign up using Facebook

This field can be retrieved by calling Class.getDeclaredField("this$0"). I've used similar production code multiple times. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. This is only possible if you can modify the concrete subclasses.

He is a Java enthusiast with particular interests in byte code engineering, functional programming, multi-threaded applications and the Scala language. Note: this requires that you instantiate a subclass of GenericClass so it can bind the type parameter correctly. Email address: 4 comments Jörgen December 27th, 2013 at 3:48 pmThanks for the post. Java is a trademark or registered trademark of Oracle Corporation in the United States and other countries.

Type Parameter is unknown.