package com.github.davidmoten.guavamini;
   
   public final class Optional<T> {
   
       private final T value;
       private final boolean present;
   
       private Optional(T value, boolean present) {
           this.value = value;
          this.present = present;
      }
  
      private Optional() {
          //no-arg constructor to enable kryo (a bit yukky but not a big deal)
          this(null, false);
      }
  
      public boolean isPresent() {
          return present;
      }
  
      public T get() {
          if (present)
              return value;
          else
              throw new NotPresentException();
      }
  
      public T or(T alternative) {
          if (present)
              return value;
          else
              return alternative;
      }
  
      public static <T> Optional<T> fromNullable(T t) {
          if (t == null)
              return Optional.absent();
          else
              return Optional.of(t);
      }
  
      public static <T> Optional<T> of(T t) {
          return new Optional<T>(t, true);
      }
  
      public static <T> Optional<T> absent() {
          return new Optional<T>();
      }
  
      public static class NotPresentException extends RuntimeException {
  
          private static final long serialVersionUID = -4444814681271790328L;
  
      }
  
      @Override
      public String toString() {
          return present ? String.format("Optional.of(%s)", value) : "Optional.absent";
      }
  }