如何测试一个Java类是否在运行时扩展了另一个？

Question

How to I test if a is a subclass of b ?

Class<?> a = A.class;
Class<?> b = B.class;

Answer 1

您是否在寻找：

Super.class.isAssignableFrom(Sub.class)

Answer 2

If you want to know whether or not a Class extends another, use Class#isAssignableFrom(Class) . For your example, it would be:

if(B.class.isAssignableFrom(A.class)) { ... }

If you're interested in whether or not an instance is of a particular type, use instanceof :

A obj = new A();
if(obj instanceof B) { ... }

Note that these will return true if the class/instance is a member of the type hierarchy and are not restrictive to direct superclass/subclass relationships. For example:

// if A.class extends B.class, and B.class extends C.class
C.class.isAssignableFrom(A.class); // evaluates to true
// ...and...
new A() instanceof C; // evaluates to true

If you want to check for direct superclass/subclass relationships, Tim has provided an answer as well.

Answer 3

You want to know if b is assignable from a :

b.isAssignableFrom(a);

Additionally, if you want to know that a is a direct subclass of b :

a.getSuperclass().equals(b);