Question

Say suppose I have the following Java code.

    public class Example {
        public static void main(String[] args){
            Person person = new Employee();
        }
    }

How to find out whether the Person is a class or an interface?

Because the Employee class can extend it if it’s a class, or implement it if it’s an interface.

And in both cases Person person = new Employee(); is valid.

Answer 1

If you don’t already know whether Person is an interface or a class by nature of the documentation for the class/interface itself (you’re using it, presumably you have some docs or something?), you can tell with code:

if (Person.class.isInterface()) {
   // It's an interface
}

Details here.

Edit: Based on your comment, here’s an off-the-cuff utility you can use:

public class CheckThingy
{
    public static final void main(String[] params)
    {
        String name;
        Class  c;

        if (params.length < 1)
        {
            System.out.println("Please give a class/interface name");
            System.exit(1);
        }
        name = params[0];
        try
        {
            c = Class.forName(name);
            System.out.println(name + " is " + (c.isInterface() ? "an interface." : "a class."));
        }
        catch (ClassNotFoundException e)
        {
            System.out.println(name + " not found in the classpath.");
        }
        System.exit(0);
    }
}

Usage:

java CheckThingy Person