Java编译器为什么不能从另一个文件中找到类？

Question

So, Main.java calls class House from House.java , one of the methods of House.class is supposed call a method from class Appointment extends Succession , which is located in Succession.java .

But for some reason, the compiler doesn't find Appointment and assumes it must be a missing variable, why? If I move the Appointment-class to Main.java or give it its own file, the compiler finds it.

I'm asking this because, I tried re-creating the error, by I haven't been able to...

House.java:

public void succession(){
    if (this.kinsmen.size() > 0){
        Appointment.callHeir(this.head, Main.human.get(1));

Succession.java:

class Appointment extends Succession {
    public static boolean callHeir(Human appointer, Human appointed){

Error:

 error: cannot find symbol
            Appointment.callHeir(this.head, Main.human.get(1));
            ^
  symbol:   variable Appointment
  location: class House

Edit full code minimized:

Main.java:

class Main {
    public static void main(String[] args) {
        House.succession();
    }
}

House.java:

public class House {
    public static void succession() {
        Appointment.callHeir();
    }
}

Succession.java:

class Succession{

}

class Appointment extends Succession {
    public static void callHeir(){
    }
}

Answer 1

I'm not sure but this might be the reason:

When compiling Main.java it encounters House.succession() .
It doesn't find House.class so it looks for and compiles House.java .

When compiling House.java it encounters Appointment.callHeir() .
It doesn't find Appointment.class so it looks for Appointment.java which doesn't exist.

When I change House.java like this

public class House {
    public static void succession() {
        Succession dummy;
        Appointment.callHeir();
    }
}

everything works fine.
This because it encounters Succession dummy first which makes the compiler look for Succession.java . Compiling that file, we automatically obtain Appointment.class .

As already suggested by others, I strongly recommend to put the Appointment class in its own file.

Answer 2

Set Access Modifier/specifier of Appointment class as public . Because by default access modifier/specifier of any class is default which doesnot allow access the class from another class.

Make Sure if you need to access the class from outside the class the access modifier/specifier of class will be public.