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

SE450: Singleton: Often the singleton is public [17/32]

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

package singleton.pub;
public interface S {
  public static final S instance =
      ("linux".equals(System.getProperty("os.name"))) ? new SLinux() : new SOther();
      public int inc();
}
final class SLinux implements S {
  private int i;
  public int inc() {return ++i;}
}
final class SOther implements S {
  private int i;
  public int inc() {return --i;}
}

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

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

If you make the singleton field public, then it should be final.

If a field is final, then it must be assigned in the initializer.