使用Java，如何在不重复比较的情况下将HashMap中的每个条目与同一HashMap中的其他每个条目进行比较？

Question

我目前正在使用2 for循环比较所有条目，但是我得到了重复的比较。因为HashMap没有排序，所以我不知道如何消除已经进行的比较。例如，我有类似的东西：

    for(Entry<String, String> e1: map.entrySet())
    { 
        for(Entry<String, String> e2: map.entrySet())
        {    
          if (e1.getKey() != e2.getKey())
            {
           //compare e1.getValue() to e2.getValue() 
            }
        }
     }

问题在于，将第一个条目与第二个条目进行比较，然后将第三个条目进行比较，依此类推。但是，第二个条目将再次与第一个条目进行比较，依此类推。然后将第三个条目与第一个条目进行比较，然后将第二个条目与第四个条目进行比较，等等。是否有更好的方法来遍历HashMaps以避免进行重复比较？

附加信息：

To be more specific and hopefully answer your questions, the HashMap I have is storing file names (the keys) and file contents (the values) - just text files. The HashMap has been populated by traversing a directory that contains the files I will want to compare. Then what I am doing is running pairs of files through some algorithms to determine the similarity between each pair of files. I do not need to compare file 1 to file 2, and then file 2 to file 1 again, as I only need the 2 files to be compared once. But I do need every file to be compared to every other file once. I am brand new to working with HashMaps. agim’s answer below might just work for my purposes. But I will also try to wrap my brain around both Evgeniy Dorofeev and Peter Lawrey's solutions below. I hope this helps to explain things better.

Answer 1

如果您不小心，则消除重复项的成本可能至少比键的冗余比较的成本高。

您可以使用以下命令订购钥匙 System.identityHashCode(x)

for(Map.Entry<Key, Value> entry1: map.entrySet()) {
   Key key1 = entry1.getKey();
   int hash1 = System.identityHashCode(key1);
   Value value1 = entry1.getValue();
   for(Map.Entry<Key, Value> entry2: map.entrySet()) {
       Key key2 = entry2.getKey();
       if (key1 > System.identityHashCode(key2)) continue;

       Value value2 = entry1.getValue();
       // compare value1 and value2;
   }
}