Tag: generics

Java erasure with generic overloading (not overriding)

I have FinanceRequests and CommisionTransactions in my domain. If I have a list of FinanceRequests each FinanceRequest could contain multiple CommisionTransactions that need to be clawed back. Dont worry how exactly that is done. The class below (very bottom) makes me feel all fuzzy and warm since its succint and reuses existing code nicely. One problem Type erasure. They both

Generic type as parameter in Java Method

generics java methods

Do you think it is possible to create something similar to this? Answer Yes, you can. Usage example:

Java override abstract generic method

abstract-class custom-attributes generics java

I have the following code However I don’t know how to do this, as I cannot override doEventStuff with something specific. Does anyone know how to do this? Answer It’s not really clear what you’re trying to do, but perhaps you just need to make Event itself generic:

Getting the class of the components of an array

arrays generics java

If I have how can I get T.class from array? If I do array.getClass() that gets me T[].class instead. Answer Component Type Use this: Returns the Class representing the component type of an array. If this class does not represent an array class this method returns null. Reference: Class.getComponentType() Safe / Unsafe casting Is there a way I can cast

Why shouldn’t Java enum literals be able to have generic type parameters?

enums generics java

Java enums are great. So are generics. Of course we all know the limitations of the latter because of type erasure. But there is one thing I don’t understand, Why can’t I create an enum like this: This generic type parameter <T> in turn could then be useful in various places. Imagine a generic type parameter to a method: Or

Why doesn’t this generic cast fail?

casting generics java

I’d expect this code to throw a ClassCastException: But it doesn’t. Casting String to T doesn’t fail, until I use the returned object somehow, like: Background: I created a Class which uses JAXB to unmarshal an XML file. It looks like this: Depending on whether the root-Element is an anonymous type or not, either T or JAXBElement is being returned.

Java generics super keyword

generics java

I went through these topics Generics..? Super T Bounding generics with ‘super’ keyword However, I still seem to be kind of lost with super keyword: When we declare a collection like that: shouldn’t it be the opposite – we have a list that contains some objects (of unknown type) which are parents of Number. So Object should fit (since it

How to cast a list of inheriting objects to a collection of objects in Java?

collections generics java

I’ve a collection type: And I’ve a list in my object: Where B is extending A But I can’t do the following: I can’t understand why since Collection is implemented by List. Answer Let’s assume for a moment you could do what you describe: The method call collecA.add(new A()) appears okay since collecA is a collection that holds As. However,

java generics covariance

alias covariance generics java

I am having trouble understanding the following article: http://www.ibm.com/developerworks/java/library/j-jtp01255.html Under, Generics are not covariant the author states, Because ln is a List, adding a Float to it seems perfectly legal. But if ln were aliased with li, then it would break the type-safety promise implicit in the definition of li — that it is a list of integers, which is

Get generic type of java.util.List

generics java

I have; List stringList = new ArrayList(); List integerList = new ArrayList(); Is there a (easy) way to retrieve the generic type of the …