title: MongoDb's $set equivalent in its java Driver
body: <p>Is there a way in which I can modify the value of one of the keys in MongoDb via its Java Driver. I tried out the following:</p>
  
  <pre><code>someCollection.update(DBObject query, DBObject update);
  someCollection.findAndModify(DBObject query, DBObject update);
  </code></pre>
  
  <p>But both the functions completely replace the queried document with the updated document. What is the way to update only one of the value of a particular key as in the case of using $set in the mongo shell.(apart from making a completely new Document with all fields copied and one of the fields updated). </p>