Do constructors always have to be public? [duplicate]

Answer 1

No,Constructors can use any access modifier, including private. (A private constructor means only code within the class itself can instantiate an object of that type, so if the private constructor class wants to allow an instance of the class to be used, the class must provide a static method or variable that allows access to an instance created from within the class.)

Example

class Alpha {
   static String s = " ";
   protected Alpha() { s += "alpha "; }
 }
 class SubAlpha extends Alpha {
   private SubAlpha() { s += "sub "; }
 }
 public class SubSubAlpha extends Alpha {
   private SubSubAlpha() { s += "subsub "; }
   public static void main(String[] args) {
     new SubSubAlpha();
     System.out.println(s);
   }
 }

Output of above program will be

alpha subsub