Why doesn't the class containing main have to be public?

Question

I declared the following class

class A { //not public
  public static void main(String args[]) {
     System.out.println(\"done\");
 }

When

Answer 1

The reason the JVM can see a non-public class is because it controls visibility, meaning it sees everything and decides what can see/call/access what.

The use of public on a class is different than on a method, but the concept is the same.

On a method, the public keyword means the method can be used outside the class. An example would be:

class A {
  public static void do() {
    // Do something
  }
}

class B {
  public static void main(String[] args) {
    A.do(); // This works because do() is public and static
  }
}

The same concept applies to classes, but in a different way.

Using public on a class means that it can be used outside the current .java file (it will have its own .class file).

Here's an example:

//C.java

  class C {
    static void do() {
      // Do something
    }

    public static void run() {
      A.do();  // Works because A.do() is public and static
      B.do();  // Does not work because B is not a public class
    }
  }



//A.java

  public class A {
    public static void main(String[] args) {
      B.do(); // Works because B is in the same file
      do();   // Duh...
    }

    public static void do() {
      // Do something
    }
  }

  class B {
    static void do() {
      // Do something
    }
  }