how do I get the simple name of a java.lang.reflect.Type in java

Question

public String getSimpleName(Type type){
    //how?
}

I can't controll variable passed into getSimpleName(Type type) except that it is instance of Type.

Of course I know that I can use p.getType().getSimpleName() in the following example, but it's not important to solve the following exmaple. what I want to show from it is that if the user (out of my control) passes p.getParameterizedType() calling getSimpleName(Type type),he still can get correct result (i.e. List).

public class App {

    public static void main(String[] args) throws NoSuchMethodException {
        final Method m = App.class.getMethod("foo", List.class);
        final Parameter p = m.getParameters()[0];
        System.out.println(p.getParameterizedType());
    }

    public void foo(List<String> strings){
    }
}

the above will print "java.util.List<java.lang.String>", but I want to get "List".

import java.lang.reflect.Method;
import java.lang.reflect.Parameter;
import java.util.List;

public class App {

    public static void main(String[] args) throws NoSuchMethodException {
        final Method m = App.class.getMethod("foo", List.class);
        final Parameter p = m.getParameters()[0];
        System.out.println(((Class<?>)p.getParameterizedType()).getSimpleName());
    }

    public void foo(List<String> strings){
    }
}

the above will throw java.lang.ClassCastException.

Exception in thread "main" java.lang.ClassCastException: sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl cannot be cast to java.lang.Class

Thanks a lot.

Does this answer your question? [Get type of a generic parameter in Java with reflection](https://stackoverflow.com/questions/1901164/get-type-of-a-generic-parameter-in-java-with-reflection) — fantaghirocco, Jul 22 '20 at 10:12
No. That's getting the type of the parameter not the generic type. — Stephen C, Jul 22 '20 at 10:16

deadshot · Answer 1 · 2020-07-22T10:29:45.883

2

You can use getType() and getSimpleName() methods.

System.out.println(p.getType().getSimpleName());

Output:

List

edited Jul 22 '20 at 10:29

answered Jul 22 '20 at 10:20

deadshot

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I can't limit the variable passed into `public String getSimpleName(Type type)` except that it is instance of Type – goushiso Jul 22 '20 at 10:54

score 2 · Accepted Answer · answered Jul 22 '20 at 10:21

There are two approaches to getting a what you want from a Type.

Cast the Type object to a ParameterizedType and call getRawType on it.

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

public class App {

    public static void main(String[] args) throws NoSuchMethodException {
        final Method m = App.class.getMethod("foo", List.class);
        final Parameter p = m.getParameters()[0];
        System.out.println(((ParameterizedType) p.getParameterizedType()).getRawType());
    }

    public void foo(List<String> strings){
    }
}

That outputs "interface java.util.List". Not exactly what you want, but closer.

Use a regex to extract the name you want from "java.util.List<java.lang.String>".

But as @deadshot points out, you can get the Class for a Parameter using getType() and then get the name of that via the Class API.

Not sure if it's guaranteed (probably not), but in this case it appears `ParameterizedType#getRawType()` returns an instance of `Class`, which means `getSimpleName()` can be used directly. — Slaw, Jul 22 '20 at 11:22

how do I get the simple name of a java.lang.reflect.Type in java

2 Answers2