Hadoop MapReduce迭代reduce调用的输入值(Hadoop MapReduce iterate over input values of a reduce call)

 我正在测试一个简单的mapreduce应用程序，但是当我迭代reduce调用的输入值时，我试图理解发生了什么。 
 
 这是一段表现奇怪的代码。 
 
public void reduce(Text key, Iterable<E> values, Context context)
    throws IOException, InterruptedException{

    Iterator<E> iterator = values.iterator();
    E first = (E)statesIter.next();

    while(statesIter.hasNext()){
        E state = statesIter.next();

        System.out.println(first.toString());
        // some other stuff
    }
    // some other stuff
}
 
 所以没什么奇怪的..除了每个println调用实际打印不同的字符串这一事实。 因此，每次调用next()方法时， first引用的对象都会更改。 
 
 那为什么这种奇怪的行为？ 

I'm testing a simple mapreduce application, but I'm getting a little stuck trying to understand what happen when I iterate over input values of a reduce call.
 
This is the piece of code which behaves strangely..
 
public void reduce(Text key, Iterable<E> values, Context context)
    throws IOException, InterruptedException{

    Iterator<E> iterator = values.iterator();
    E first = (E)statesIter.next();

    while(statesIter.hasNext()){
        E state = statesIter.next();

        System.out.println(first.toString());
        // some other stuff
    }
    // some other stuff
}
 
so nothing strange.. except the fact that each println invocation actually prints a different string. So, every time I call the next() method, the object referenced by first changes.
 
So why this strange behavior?

原文：https://stackoverflow.com/questions/15976981