title: MapReduce with Hadoop: Type mismatch in key from map
body: <p>I'm running a simple wordcount program, and I get the following error:</p>
  
  <pre><code>Type mismatch in key from map: expected org.apache.hadoop.io.Text, received org.apache.hadoop.io.LongWritable
  </code></pre>
  
  <p>What is the meaning of this, and how do I rectify it??</p>