如何将记录放入LinkedHashMap Java映射中或如何创建数据结构？

Question

How to put record in :

Map<String, LinkedHashMap<String, String>> fileRecords = new LinkedHashMap<String, LinkedHashMap<String,String>>();

I have two files in the same format, i have to create the data structure for both of them, and then compare the data structure to identify the differences for each CAID-find the blocks and compare the data.

So accordingly i tried to read the file line by line. confused of what should i try to put the records in map or in arraylist (I have to follow the insertion order).

Take ID as unique, for unique id, i want to store the corresponding block and data.

Answer 1

The decision to use a Map or a List or a Set lies on the purpose of the data being read.

• if you need to index the data (eg by ID), then use a Map
• else, if you want to iterate through the data in order, I would recommend a List or Set collection. If your dataset does not support duplicates I recommend you a Set, or a List if it will have duplicates.

About the code using Map, the piece of code below groups Block and Data per ID:

public void read() {
   Map<String, LinkedHashMap<String, String>> fileRecords = new LinkedHashMap<>();
   String id, block, data;

   //while(dataInFile()) {
       // I assume data is read row by row into vars id, block and data

       // get the block map for the just read ID
       LinkedHashMap<String, String> blockRecords = fileRecords.get(id);

       // first Block for the ID
       if (blockRecords == null) {
           blockRecords = new LinkedHashMap<>();
           fileRecords.put(id, blockRecords);
       }

       // read data and block
       blockRecords.put(block, data);
   }

This code also allows you to group block and data if the IDs are not sorted in the file. If the ID is always an integer, I recommend you to use an Integer instead of String. It saves memory and CPU during the matching.

Also, if data in your file is not just these 3 fields, I'd recommend you to use objects instead. Then you will need to be more mindful about the usage of the data to design the object model.