Class type injection in Spring xml vs java config

Question

Class X{
   Class<B> object;
   public setObject( Class<B> a ){....}
}

Interface B{}
Interface C extends B {}

I instantiate X like this,

X x = new X();
x.setObject( C.class );

When i build the code it complains required Class<B> found Class<C>. Since C extends B, can i not use C.class? If so can some one explain why?

I i do the same thing using Spring`s XML based bean creating it works just fine. The bean definition would be

<bean id="dummy" class="X">
<property name"object" value="C">
</bean>

This works just fine. Im not getting why instantiating in java would fail.

Answer 1

this is not valid Java code

It works because there is type erasure done for parameters <>

the java bytecode looks exactly the same as the one for

class X{
   Class object;
   public void setObject( Class a ){....}
}

interface B{}
interface C extends B {}

It looses the type checks information, it is only used at compile time.

You can use this to make it work in the code:

class X{
   Class<? extends B> object;
   public void setObject( Class<? extends B> a ){....}
}

interface B{}
interface C extends B {}