MapReduce with Hadoop: Type mismatch

I'm running a simple hadoop program, and I get the following error:

java.io.IOException: Type mismatch in key from map: expected org.apache.hadoop.io.Text, recieved org.apache.hadoop.io.LongWritable

Mapper:

public static class myMapper extends Mapper<LongWritable, Text, Text, Text>
public void map(LongWritable key, Text line,OutputCollector<Text,Text> output, Reporter reporter) throws IOException, InterruptedException

Reducer:

public static class triangleCounterReducer extends Reducer<Text, Text, Text, Text> 
public void reduce(Text key,Iterable<Text> line,OutputCollector<Text,Text> output,Reporter reporter) throws IOException, InterruptedException

Main:

...
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(Text.class);
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(Text.class);
...

How can i fix this????

Copyright Notice：Content Author:「Babis Babis」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/14665711/mapreduce-with-hadoop-type-mismatch