SE450: Often the singleton is public [2015/11/03]

SE450: Singleton: Often the singleton is public [19/32]

file:S.java [source] [doc-public] [doc-private]

package singleton.pub3;
public abstract class S {
  private static S newS() {
    if ("linux".equals(System.getProperty("os.name")))
      return new SLinux();
    else
      return new SOther();
  }
  public static final S instance = newS();
  public abstract int inc();
}
final class SLinux extends S {
  private int i;
  public int inc() {return ++i;}
}
final class SOther extends S {
  private int i;
  public int inc() {return --i;}
}

file:Main.java [source] [doc-public] [doc-private]

package singleton.pub3.main;
import singleton.pub3.S;
public class Main {
  public static void main (String[] args) {
    S s = S.instance;
    System.out.println(s.inc());
    System.out.println(s.inc());
  }
}

It's a bit more natural using an abstract class.

(I dislike java's restrictions on static members in interfaces.)