Get generic type of java.util.List

If those are actually fields of a certain class, then you can get them with a little help of reflection:

package test;

import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.util.ArrayList;
import java.util.List;

public class Test {

    List<String> stringList = new ArrayList<String>();
    List<Integer> integerList = new ArrayList<Integer>();

    public static void main(String... args) throws Exception {
        Field stringListField = Test.class.getDeclaredField("stringList");
        ParameterizedType stringListType = (ParameterizedType) stringListField.getGenericType();
        Class<?> stringListClass = (Class<?>) stringListType.getActualTypeArguments()[0];
        System.out.println(stringListClass); // class java.lang.String.

        Field integerListField = Test.class.getDeclaredField("integerList");
        ParameterizedType integerListType = (ParameterizedType) integerListField.getGenericType();
        Class<?> integerListClass = (Class<?>) integerListType.getActualTypeArguments()[0];
        System.out.println(integerListClass); // class java.lang.Integer.
    }
}

You can also do that for parameter types and return type of methods.

But if they're inside the same scope of the class/method where you need to know about them, then there's no point of knowing them, because you already have declared them yourself.

You can do the same for method parameters as well:

Method method = someClass.getDeclaredMethod("someMethod");
Type[] types = method.getGenericParameterTypes();
//Now assuming that the first parameter to the method is of type List<Integer>
ParameterizedType pType = (ParameterizedType) types[0];
Class<?> clazz = (Class<?>) pType.getActualTypeArguments()[0];
System.out.println(clazz); //prints out java.lang.Integer

Short answer: no.

This is probably a duplicate, can't find an appropriate one right now.

Java uses something called type erasure, which means at runtime both objects are equivalent. The compiler knows the lists contain integers or strings, and as such can maintain a type safe environment. This information is lost (on an object instance basis) at runtime, and the list only contain 'Objects'.

You CAN find out a little about the class, what types it might be parametrized by, but normally this is just anything that extends "Object", i.e. anything. If you define a type as

class <A extends MyClass> AClass {....}

AClass.class will only contain the fact that the parameter A is bounded by MyClass, but more than that, there's no way to tell.