Starting with JDK 12, we can obtain the type descriptor of a class as a String object via the Class.descriptorString() method:

// Lmodern/challenge/Pair;
System.out.println("Type descriptor of Pair: " 
  + clazz.descriptorString());

// Ljava/lang/String;
System.out.println("Type descriptor of String: " 
  + String.class.descriptorString());