可迭代到 ArrayList 元素更改 [英] Iterable to ArrayList elements change

问题描述

所以我正在实施一个 mapreduce 工作，这意味着我正在处理键值对.

So I am implementing a mapreduce job which means I am dealing with key value pairs.

我有变量

Iterable<FreqDataWritable> values

FreqDataWritable 是一个包含信息片段的对象，但现在我只关心它保存的一条信息，它是一个由 getFilename() 访问的字符串.

FreqDataWritable is an object that contains pieces of information, but for now I am only concerned with one piece of information it holds which is a String which is accessed by getFilename().

我有以下循环:

ArrayList<String> filenames = new ArrayList<String>();

for(FreqDataWritable i : values) {
    filenames.add(i.getFilename());
}

现在我要做的就是打印数组列表文件名中的值.

Now all I want to do is print the values in the array list filenames.

for(int i = 0; i < filenames.size(); i++) {
    System.out.println(filenames.get(i));
}

但是，当我这样做时，文件名中的所有内容都是相同的.唯一打印出来的是一个文件名多次打印.

However when I do this everything in filenames is the same. The only thing printed out is a single filename printed multiple times.

我的原始代码比这更复杂，但我简化了它以寻求帮助.有人知道怎么修这个东西吗?

My original code is more complex than this, but I simplified it for help. Anyone know how to fix this?

谢谢

推荐答案

我想通了.Hadoop 的内存使用量很奇怪，所以当我第一次迭代这些值时，它只是一遍又一遍地将相同的对象添加到数组列表中.

I figured it out. Hadoop has an odd memory usage so when I iterated over the values the first time it was just adding the same object over and over again to the arraylist.

相反，我需要这样做:

for(FreqDataWritable i : values) {
    filenames.add(new String(i.getFilename()));
}

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