Don't make the new class public and you could use its name to call the methods inside the new class from your main.
public class Main
{
public static void main(String[] args) {
System.out.println("Hello World");
newclass.newmethod();
}
}
class newclass
{
public static void newmethod() {
System.out.println("This is from the new class' new method");
}
}
Or you could use a static object to do it (e.g. static newclass obj = new newclass(); to create an object and obj.newmethod() to call the method.)