在java中传递Class对象

Question

I have an Interface and 2 concrete class that implement that interface,

public interface ITemplate{}

public Template implements ITemoplate {}
public Template2 implements ITemplate {}

I have a method that takes in the Class object and instantiates it.

public addTemplate(Class<ITemplate> template){
    pipe.add(template.newInstance())
}

The problem is that when I call that method, it throws a compile time error:

instance.addTemplate(Template.class)

Compile Time Error :

addTemplate(java.package.ITemplate.class) cannot be applied to addTemplate(java.package.Template.class)

Am I missing something, or is there a work around for this?

Answer 1

Class<ITemplate> will strictly accept the ITemplate.class

Class<? extends ITemplate> Class<? extends ITemplate> will accept any of the classes implementing ITemplate.class

Answer 2

try this method:

// works for all classes that inherit from ITemplate.
public addTemplate(Class< ? extends ITemplate> template){ 
    pipe.add(template.newInstance())
}

instead of

// only accepts ITemplate Type Class (Strict Type).
public addTemplate(Class<ITemplate> template){ 
    pipe.add(template.newInstance())
}

Here is an explanation: when you use Class<ITemplate> it is a strict type of class Itemplate . It will never take any other type argument other than ITemplate , because it is resolved at compile time only. However Class <? extends ITemplate> Class <? extends ITemplate> can accept all objects that are either ITemplate or have ITemplate as a superclass.