public class IntSortReducer extends Reducer<IntWritable, IntWritable, IntWritable, IntWritable> { private static final IntWritable lineNumber = new IntWritable(0); private int count = 0; @Override protected void reduce(IntWritable key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException { // ignore values: they'll always be 1 (as long as paired with IntMapper) synchronized (lineNumber) { /* TODO: Advance line number */ context.write(/* TODO: Write new, reduced <K,V> pair to context */lineNumber,key); count++; lineNumber.set(count); } } }

这段代码是一个 MapReduce 程序中的 Reduce 阶段的代码，它的作用是将相同的键值对进行合并，并输出一个新的键值对。该程序的输入键值对类型是 IntWritable，输出键值对类型也是 IntWritable。

具体来说，该程序使用 reduce() 方法对每个键值对进行处理。在 reduce() 方法中，忽略输入的 values 值，因为在该程序的 Map 阶段中，每个键值对的 values 都被设置为 1。

在该程序中，使用 synchronized 关键字保证了 lineNumber 的线程安全，同时使用 count 计数器记录已经处理的键值对数量。在 reduce() 方法中，通过调用 context.write() 方法将新的键值对写入到 context 中。其中，第一个参数是新生成的键值对的键值，第二个参数是新生成的键值对的值。在该程序中，新生成的键值对的键为 lineNumber，值为原始键值对的键。

最后，通过调用 set() 方法将 lineNumber 的值设置为 count，以便下一次生成新的键值对时使用更新后的 lineNumber 值。

相关问题

public class IntSortReducer extends Reducer<IntWritable, IntWritable, IntWritable, IntWritable> { private static final IntWritable lineNumber = new IntWritable(0); @Override protected void reduce(IntWritable key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException { // ignore values: they'll always be 1 (as long as paired with IntMapper) synchronized (lineNumber) { /* TODO: Advance line number */ context.write(/* TODO: Write new, reduced <K,V> pair to context */); } } }

补全后的代码如下：

public class IntSortReducer extends Reducer<IntWritable, IntWritable, IntWritable, IntWritable> {
    private static final IntWritable lineNumber = new IntWritable(0);
    private int count = 0;
    
    @Override
    protected void reduce(IntWritable key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
        // ignore values: they'll always be 1 (as long as paired with IntMapper)
        synchronized (lineNumber) {
            /* Advance line number */
            count++;
            lineNumber.set(count);
            /* Write new, reduced <K,V> pair to context */
            context.write(lineNumber, key);
        }
    }
}

在补全的代码中，我们通过使用 count 计数器和线程安全的 synchronized 关键字来实现了一个自增的 lineNumber，然后将新生成的键值对通过调用 context.write() 写入到 context 中。

补全public class IntSortReducer extends Reducer<IntWritable, IntWritable, IntWritable, IntWritable> { private static final IntWritable lineNumber = new IntWritable(0); @Override protected void reduce(IntWritable key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException { // ignore values: they'll always be 1 (as long as paired with IntMapper) synchronized (lineNumber) { /* TODO: Advance line number */ context.write(/* TODO: Write new, reduced <K,V> pair to context */); } } }

补全后的代码如下：

public class IntSortReducer extends Reducer<IntWritable, IntWritable, IntWritable, IntWritable> {
    private static final IntWritable lineNumber = new IntWritable(0);
    private int count = 0;
    
    @Override
    protected void reduce(IntWritable key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
        // ignore values: they'll always be 1 (as long as paired with IntMapper)
        synchronized (lineNumber) {
            /* Advance line number */
            count++;
            lineNumber.set(count);
            /* Write new, reduced <K,V> pair to context */
            context.write(lineNumber, key);
        }
    }
}

在补全的代码中，我们通过使用 count 计数器和线程安全的 synchronized 关键字来实现了一个自增的 lineNumber，然后将新生成的键值对通过调用 context.write() 写入到 context 中。