java/src/main/com/google/appengine/api/datastore/ReadPolicy.java

   1 // Copyright 2010 Google Inc. All Rights Reserved.
   2
   3 package com.google.appengine.api.datastore;
   4
   5 /**
   6  * Policy for reads.
   7  *
   8  */
   9 public final class ReadPolicy {
  10
  11   /**
  12    * Setting the {@code Consistency} for reads allows you to decide whether
  13    * freshness or availability is more important.
  14    */
  15   public enum Consistency {
  16
  17     /**
  18      * Selects freshness over availability.  Strongly consistent reads are
  19      * guaranteed to return the most up-to-date data but will timeout more
  20      * often than eventually consistent reads.
  21      */
  22     STRONG,
  23
  24     /**
  25      * Selects availability over freshness.  Eventually consistent reads will
  26      * timeout less often than Strong reads but will occasionally return
  27      * stale results.
  28      */
  29     EVENTUAL
  30   }
  31
  32   private final Consistency consistency;
  33
  34   public ReadPolicy(Consistency consistency) {
  35     if (consistency == null) {
  36       throw new NullPointerException("consistency must not be null");
  37     }
  38     this.consistency = consistency;
  39   }
  40
  41   public Consistency getConsistency() {
  42     return consistency;
  43   }
  44
  45   @Override
  46   public boolean equals(Object o) {
  47     if (this == o) {
  48       return true;
  49     }
  50     if (o == null || getClass() != o.getClass()) {
  51       return false;
  52     }
  53
  54     ReadPolicy that = (ReadPolicy) o;
  55
  56     if (consistency != that.consistency) {
  57       return false;
  58     }
  59
  60     return true;
  61   }
  62
  63   @Override
  64   public int hashCode() {
  65     return consistency.hashCode();
  66   }
  67 }