Check if an object is instance of List of given class name

Question

Given an Object o and a String className = "org.foo.Foo", I want to check if o is instance of List<className>

I tried this but won't compile:

Class<?> cls = Class.forName(className);
if (o instanceof List<cls>){ // this gives error: cls cannot be resolved to a type
  doSomething();
}

Please note that my inputs are Object o and String className (please mind types).

Answer 1

It's because of Type Erasure. The statement

if (o instanceof List<cls>) {
  doSomething();
}

will be executed at runtime, when the generic type of the list will be erased. Therefore, there's no point of checking for instanceof generic-type.

Answer 2

I think you can do it in two steps: First, you check it's a List.

if (o instanceof List)

Then, you check that one (each?) member of the list has the given type.

for (Object obj : (List) o) {
    if (obj instanceof cls) {
        doSomething();
    }
}

Answer 3

Ok, I found a method... it's a little dirty code but it works:

if (o instanceof List<?>){
  ParameterizedType pt = (ParameterizedType)o.getClass().getGenericSuperclass();
  String innerClass = pt.getActualTypeArguments()[0].toString().replace("class ", "");
  System.out.println(innerClass.equals(className)); // true
}