How JAVA uses ParameterizedType in classes to get generic types

use ParameterizedType in the class to get the generic class of the entity class of the class
has the following code:

public class Demo<T> {
    
    private Class<T> clazz;
    
    public T getDemo() throws InstantiationException, IllegalAccessException{
        return clazz.newInstance();
    }

    public static void test() throws InstantiationException, IllegalAccessException{
        String str = new Demo<String>().getDemo();
    }
    
}

now I"m going to call the test () method to get a String entity class, but when I call it, I throw a NullPointerException indicating that clazz is null and cannot be called. So at this point I"ll change the getDemo method, use ParameterizedType to get the generics and assign

    public T getDemo() throws InstantiationException, IllegalAccessException{
        Type superClass = getClass();
        if(superClass instanceof ParameterizedType){
            Type type = ((ParameterizedType) superClass).getActualTypeArguments()[0];
            this.clazz = (Class<T>) type;
        }else{
            System.out.println("");
        }
        return clazz.newInstance();
    }

but the superClass obtained at this time is Demo, not Demo < String >, so the superClass instanceof ParameterizedType is not valid, the console output is "not equal", and the clazz is still not null, so I would like to ask you how to get generic classes in this case.

Note that it is useless to change Type superClass = getClass (); to Type superClass = getClass (). GetGenericSuperclass ();, because the Demo class does not inherit other classes, so getting Object, is not equal.

public class Demo<T> { private Class<T> clazz; public T getDemo() throws InstantiationException, IllegalAccessException{ Type superClass = getClass().getGenericSuperclass(); if(superClass instanceof ParameterizedType){ Type type = ((ParameterizedType) superClass).getActualTypeArguments()[0]; this.clazz = (Class<T>) type; }else{ System.out.println(""); } return clazz.newInstance(); } public static void main(String[] args) throws IllegalAccessException, InstantiationException { Demo<String> MyDemo = new Demo<String>() { }; String str = MyDemo.getDemo(); System.out.println(str); } }