Java Reflection ArrayList.class.getMethod(“get”) returns NoSuchMethodException

Question

Why can't I get the "get" method of an ArrayList and invoke it?

I am using reflection to modify within my nested classes. One of my classes has a list of classes so I wanted to be able to use the same logic to get and invoke the get method.

simplified, the line that fails is

ArrayList.class.getClass().getMethod("get")

and it fails, giving me a NoSuchMethodException.

I understand that I could use aList.get() but that's not the point, I need to use reflection since this is in a deeply nested class.

TL;DR How can I get the "get" method of an array list?

Answer 1

Note that Class#getMethod() has two parameters: a String and an vararg of Class objects. The former is

the list of parameters

that the method declares.

You need to use

ArrayList.class.getMethod("get", int.class);

since the ArrayList#get(int) method has an int parameter.

---

I initially missed the whole

ArrayList.class.getClass().getMethod("get")
          ^     ^ 
          |     |----------------------------- gets Class<Class>
          |----------------------------------- gets Class<ArrayList>

The .class already gets the Class instance for ArrayList . Calling getClass on that will return the Class instance for class Class . You don't want that.

Answer 2

Method methods = ArrayList.class.getMethod("get", int.class);

您不需要在.class之后再次调用getClass（）方法，因为当您在类名之后编写.class时，它引用了表示给定类的Class对象。