java - map 比较不会产生正确的结果

Question

我有两个 HashMap FinalOldCsv 和 FinalNewCsv。这些映射存储从旧 csv 和新 csv 读取的值。下面是我的代码，用于找出常见行、仅来自旧 csv 的行和仅来自新 csv 的行。对于包含以下内容的小 csv数千行，我的代码工作正常。但是当我尝试对一百万行的 csv 执行相同的操作时。它会产生错误的结果。代码-

 private static void findDiff(LinkedHashMap<String, Integer> finalOldCsv,
            LinkedHashMap<String, Integer> finalNewCsv) {
        for(String test:finalOldCsv.keySet())
        {
        System.out.println("first row from old="+finalOldCsv.get(test));
        }
        for(String test1:finalNewCsv.keySet())
        {
        System.out.println("first row from new="+finalNewCsv.get(test1));

        }
         ArrayList<String>temp=new ArrayList<String>();
         for(String oldMatch : finalNewCsv.keySet())
         {
             if(oldMatch.contains(column[0]))
                 continue;
             else
             {
                 if (finalNewCsv.containsKey(oldMatch)&& finalOldCsv.containsKey(oldMatch))
                 {
                     System.out.println("Match Found");
                     writeCsv(writer,"Result/"+prefix+"_", oldMatch,"Common Rows");
                    temp.add(oldMatch);
                 }
             }
         }
         System.out.println("before old csv size="+finalOldCsv.size());
         for(String t:temp)
         {
         finalNewCsv.remove(t);
         finalOldCsv.remove(t);
         }
         System.out.println("after old csv size="+finalOldCsv.size());
         temp.clear();
         for(String newMatch : finalNewCsv.keySet())
           {
             if(newMatch.contains(column[0]))
            continue;
             else
             {
                 if (!finalOldCsv.containsKey(newMatch)&& finalNewCsv.containsKey(newMatch))
                 {
                 writeCsv(writer,"Result/"+prefix+"_", newMatch,"New Rows in New Table");
                 temp.add(newMatch);

                 }
             }

           }
         for(String t:temp)
         {
         finalNewCsv.remove(t);
         }
         temp.clear();
         System.out.println("finalOldCsv.keySet().size()"+finalOldCsv.keySet().size());
         for(String restFromOldTable:finalOldCsv.keySet())
         {
             if(restFromOldTable.contains(column[0]))
                 continue;
             else
                // if()
             writeCsv(writer,"Result/"+prefix+"_", restFromOldTable,"Rows from Old Table");
         }

    }

Answer 1

我认为你让事情变得更加复杂了。例如，当您在 if 语句中迭代 finalNewCsv 时，您会得到这个 finalNewCsv.containsKey(oldMatch)，这是不必要的，因为它始终为 true

整个方法可以简化为:

Iterator<Map.Entry<String, Integer>> it = oldMan.entrySet().iterator();
    while (it.hasNext()) {
        Map.Entry<String, Integer> entry = it.next();
        if (newMap.containsKey(entry.getKey())) {
            it.remove();
            commonEntries.put(entry.getKey(), entry.getValue());
            newMap.remove(entry.getKey());
        }
    }

其作用是将 oldMap 和 newMap 中所有相似的键添加到 commonEntries 映射中。我不完全确定这是否是 findDiff() 应该做的事情(该方法的名称具有误导性)。