Get TypeElement from Generic TypeParameterElement for Java Annotation Processor?

Question

Using Java Annotation Processors I have the following type:

@NameToken(value={"startPage"})
public interface MyProxy extends Proxy<StartPagePresenter> {
}

and:

public interface Proxy<T> { }

I have the TypeElement of Proxyas:

TypeElement pProxyTypeElement = // ...

Now I want to get the TypeElement of the Type Parameter <StartPagePresenter>.

I tried:

List<? extends TypeParameterElement> proxyTypeParamElems = 
                                         proxyTypeElement.getTypeParameters();
TypeParameterElement firstParameter = proxyTypeParamElems.get(0);

When I print firstParameter.getSimpleName() I get T instead of StartPagePresenter.

How do I get the real TypeElement StartPagePresenter from the TypeParameter?

score 9 · Accepted Answer · answered Apr 28 '15 at 15:24

To access the generic paramters, you'll need the TypeMirror cast to a DeclaredType. DeclaredType has a method getTypeArguments() which returns a list of TypeMirror which represent the concrete declared generic parameters:

Following your example:

    Set<? extends Element> proxyElements = roundEnvironment.getElementsAnnotatedWith(NameToken.class);

    for(Element element : proxyElements){
        TypeElement typeElement = (TypeElement)element;
        DeclaredType declaredType = (DeclaredType)typeElement.getInterfaces().get(0); //assuming there is an interface

        for(TypeMirror genericParameter : declaredType.getTypeArguments()){
            messager.printMessage(Diagnostic.Kind.NOTE, genericParameter.toString());
        }
    }

Should print StartPagePresenter

I prefer using the various visitors supplied with the API to smooth out this casting.

nice one sir, but what about getting generic of field element? like `List mList`? — Hendra Anggrian, Apr 13 '17 at 13:23
You can get the generic parameters by calling `((TypeElement)element).getTypeParameters()` - See the OP's question for and example of this. — John Ericksen, Oct 05 '17 at 16:33

Get TypeElement from Generic TypeParameterElement for Java Annotation Processor?

1 Answers1