Question

Let’s say I have a Method:

public void method(LinkedList<Integer> intList);

I use reflection to obtain the java.lang.reflect.Method for this method, and I want to obtain the ParameterizedType, ie. LinkedList<Integer>.

Unfortunately, using Method.getParameterTypes() I can only seem to get the non-parameterized Class Class<LinkedList>.

However in my debugger if I look at the Method object I san see that there is a “signature” field that does appear to contain the generic information:

(Ljava/util/LinkedList<Ljava/lang/Integer;>;)V

So how can I obtain the LinkedList parameterized type from the Method object?

Answer 1

Use Method.getGenericParameterTypes. Sample code:

import java.lang.reflect.*;
import java.util.*;

public class Test {

    public void foo(LinkedList<Integer> intList) {
    }

    public static void main(String[] args) throws Exception {
        Method method = Test.class.getMethod("foo", LinkedList.class);
        Type[] parameters = method.getGenericParameterTypes();
        System.out.println(parameters[0]);
    }
}

Output:

java.util.LinkedList<java.lang.Integer>