如何定义类型变量以调用Java中的泛型方法

Question

Have a generic method shown below, wants to call the method with a variable which is the matching type. How to define such variable? and how to assign the type to it.

no problem calling it with C1 and C2

t.<C1> getListConfigObjects("foo", String.class);   
t.<C2> getListConfigObjects("foo", String.class);

how to define a variable to call the generics method?

how to do something like this in Java

Type <? extends JsonXformIntf> theType = C1.getType();
t.<theType> getListConfigObjects("foo", String.class);

theType = C2.getType();
t.<theType> getListConfigObjects("foo", String.class);

Answer 1

Assuming that they both compile, there is absolutely no difference between these two in terms of the compiled bytecode (and thus no possible difference in runtime behavior):

t.<C1>getListConfigObjects("foo", String.class);   
t.<C2>getListConfigObjects("foo", String.class);

Generics is compile-time only. After type erasure, they are both t.getListConfigObjects("foo", String.class); . In other words, the type argument you specify is not known to the method at runtime .

The only use of an explicitly-specified type argument is for the compiler's type-checking purposes -- explicitly specifying a right type argument will allow the compiler to compile it (whereas the compiler may otherwise infer it wrong); conversely, explicitly specifying a wrong type argument will make it not compile. However, if they both compile, then there is no difference.

Therefore, it wouldn't make sense to specify a type argument that is not known at compile-time, because compile-time is the only time when such a type argument is used at all. Simply pick any type argument that allows it to compile.