Java generics, get Class<T> of generic parameter
I have an abstract class:
public abstract class RootProcessor<T> {
Class<T> clazz;
}
I need to fill ClassT clazz;
with the children of RootProcessor
- every child has its own T
I found only one solution, but it needs compiler argument -Xlint:unchecked
public RootProcessor(){
this.clazz = (Class<T>) ((ParameterizedType) this.getClass().getGenericSuperclass()).getActualTypeArguments()[0];
}
Is this the best solution? Can we do the same without -Xlint:unchecked
?
Solution 1:
The typesafe, but boilerplatey way to do this is to pass the Class<T>
token "where the compiler can see it":
public abstract class RootProcessor<T> {
Class<T> clazz;
protected RootProcessor<T>(Class<T> clazz) {
this.clazz = clazz;
}
}
public class FooProcessor extends RootProcessor<Foo> {
public FooProcessor() {
super(Foo.class);
}
}
If you're doing an unchecked cast but you "know what you're doing" and want the compiler to stop complaining, the correct approach would be localising the non-type-safe-but-you-know-they-work bits and using @SuppressWarnings
:
public abstract class RootProcessor<T> {
Class<T> clazz;
{ initClazz(); }
@SuppressWarnings("unchecked")
private void initClazz() {
// the usual verbiage you already have in your question
this.clazz = this.getClass().getGenericSuperclass().yadda().blah();
}
}
(I won't hold this against you :P)
Solution 2:
There is a post of the same subject: Reflecting generics
And a class that implement it:TypeArgumentsUtils.java
An example is in the unit test.
So if you have this class:
public class BarProcessor extends RootProcessor<Bar> {
public BarProcessor() {
}
}
than you would get the first parameter with:
Class barClass = TypeArgumentsUtils.getFirstTypeArgument(
RootProcessor.class, BarProcessor.class);