如何将 class 类型作为参数传递给 function？

Question

I have four classes: A, B, C, D. B, C, D extends A. I have a list - List<A> that contains all kinds of objects, and I want to build a function that gets one of the classes as parameter and prints from the list all the objects that belongs to the class.

Answer 1

    public static void printElements(List<A> list, Class<? extends A> type) {
        for (A element : list) {
            if (type.isAssignableFrom(element.getClass())) {
                System.out.println(element);
            }
        }
    }

The method isAssignableFrom can be used to determine if the Class received as a parameter is the same class or a superclass of each element of the list.

The Class<? extends A> Class<? extends A> is used to only allow types that are of type A or a subclass that are the type of elements allowed in the list.

Answer 2

You could do something like this:

List<A> list = (...);

public static void print(Class klass) {
  for(A a : list) {
    if(klass.isInstance(a)) {
      System.out.println(a);
    }
  }
}

To use it:

print(C.class);

Or

C c = new C();

print(c.getClass());