java - 从存储在容器中的类构造对象

Question

这是代码:

import java.util.ArrayList;
import java.util.List;

public class Main {
    public abstract static class Base {
    }

    public static class Derived1 extends Base {
    }

    public static class Derived2 extends Base {
    }

    public static <T> T createObject(Class<T> someClass) {
        T a = null;
        try {
            a = someClass.newInstance();
        } catch (InstantiationException e) {
        } catch (IllegalAccessException e) {
        }
        return a;
    }

    public static void main(String[] args) {
        Derived2 d2 = createObject(Derived2.class);   // here it works

        // here is some array with classes
        Class[] someClasses = new Class[] { Derived1.class, Derived2.class };
        // here is some list which should be filled with objects of these classes
        List<? extends Base> l = new ArrayList();
        // in this loop, the list should be filled with objects
        for(Class c : someClasses) {
            l.add(createObject<? extends Base>(c));   // ERROR: java: illegal start of expression
        }
    }
}

上面代码中的错误就行了:

l.add(createObject<? extends Base>(c));   // ERROR: java: illegal start of expression

如何正确构造 for 循环以及如何正确调用方法 createObject 以便列表 l 中充满类的对象数组someClasses？

Answer 1

您的Class[]应该是Class<? extends Base>[] 。或者，使用 List<Class<? extends Base>> ，这不会导致泛型警告。