我正在编写一个mapper函数，它将键生成为一些用户id，值也是文本类型。我是这样做的

public static class UserMapper extends Mapper<Object, Text, Text, IntWritable> {
    private final static IntWritable one = new IntWritable(1);
    private Text userid = new Text();
    private Text catid = new Text();

    /* map method */
    public void map(Object key, Text value, Context context)
                throws IOException, InterruptedException {
        StringTokenizer itr = new StringTokenizer(value.toString(), ","); /* separated by "," */
        int count = 0;

        userid.set(itr.nextToken());

        while (itr.hasMoreTokens()) {
            if (++count == 3) {
                catid.set(itr.nextToken());
                context.write(userid, catid);
            }else {
                itr.nextToken();
            }
        }
    }
}

然后，在主程序中，我将Map器的输出类设置为：

Job job = new Job(conf, "Customer Analyzer");
    job.setJarByClass(popularCategories.class);
    job.setMapperClass(UserMapper.class);
    job.setCombinerClass(UserReducer.class);
    job.setReducerClass(UserReducer.class);

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

因此，尽管我已将输出值的类设置为text.class，但编译时仍会出现以下错误：

popularCategories.java:39: write(org.apache.hadoop.io.Text,org.apache.hadoop.io.IntWritable)
 in org.apache.hadoop.mapreduce.TaskInputOutputContext<java.lang.Object,
 org.apache.hadoop.io.Text,org.apache.hadoop.io.Text,
 org.apache.hadoop.io.IntWritable> 
 cannot be applied to (org.apache.hadoop.io.Text,org.apache.hadoop.io.Text)
 context.write(userid, catid);
                           ^

根据此错误，它仍在考虑此格式的Map器类： write(org.apache.hadoop.io.Text,org.apache.hadoop.io.IntWritable) 所以，当我如下更改类定义时，问题就解决了。

public static class UserMapper extends Mapper<Object, Text, Text, Text> {

 }

所以，我想了解类定义和设置mapper output vaue类之间的区别。