生成唯一的序列号java

Question

I generate lists based on Map,

       Map<String, List<Integer>> map = new HashMap<String, List<Integer>>();

complete code is here: https://repl.it/L3cv/0

Result of the code:

      list1: [account_number, account_number, account_number, account_number, Amount, Amount, Amount, Amount]
      list2: [1, 2, 3, 4, 100, 400, 500, 700]

Desired result: (generating unique sequence/id based on list2)

      list3: [1, 2, 3, 4, 1, 2, 3, 4]

In the code, I tried to add 'sequence_number', but it just gives the incremental value [1,2,3,4,5,6,7,8]

        sequence_number = 0;
        for (final Integer val : value) {
            sequence_number++;
            list3.add(key);
            list4.add(val);
        }

but this does not give me the desired result. How to do it?

Answer 1

There are two possible solutions, based on your answer to this question:

"Does the first list always contain pairs of items? Means, it always has an even number of entries, so if there are 12 entries, you expect 1,2,3,4,5,6,1,2,3,4,5,6?"

If yes, your solution goes like this:

 int halflist = list1.size() / 2;
 int sequencenumber = 0;
 for (...) {
    sequencenumber++;
    // add your stuff
    if (sequencenumber == halflist) sequencenumber = 0;
 }

This will raise the value 1,2,3,4,1,2,3,4. It could be done with modulo and more fancy code too, but the simple increment here should keep it understandable.

• If no, please provide more details, what you want to achieve.

Answer 2

I am not 100% sure what problem you are trying to solve. This is what I think you try to achieve.

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

class Main {
  public static void main(String[] args) {
    List<Integer> list1 = new ArrayList<Integer>();
    list1.add(1);
    list1.add(2);
    list1.add(3);
    list1.add(4);
    List<Integer> list2 = new ArrayList<Integer>();
    list2.add(100);
    list2.add(400);
    list2.add(500);
    list2.add(700);

    Map<String, List<Integer>> map = new HashMap<String, List<Integer>>();
    map.put ("account_number", list1);
    map.put ("Amount", list2);

    System.out.println(map);

    List<String> list3 = new ArrayList<String>();
    List<Integer> list4 = new ArrayList<Integer>();

    String lastkey = null;
    int sequence = 0;
    for (final Entry<String, List<Integer>> entry : map.entrySet()) {
        final String key = entry.getKey();
        final List<Integer> value = entry.getValue();

        for (final Integer val : value) {
            list3.add(key);
            if(lastkey == null||lastkey!=key){
              sequence = 1;
              lastkey = key;
            } 
            list4.add(sequence++);
        }
    }

    System.out.println(list3);
    System.out.println(list4);
  }
}

Answer 3

Desired result: (generating unique sequence/id based on list2)

Did you mean list1 ? Because the example you have given - [1, 2, 3, 4, 1, 2, 3, 4] , is of list1 .

Then, if you want to restart the sequence ID-Counter over the size of list1 , you could use % -operator:

    for (final Entry<String, List<Integer>> entry : map.entrySet()) {
        final String key = entry.getKey();
        final List<Integer> value = entry.getValue();
        for (int i = 0; i < value.size(); i++) { //<<< We need an index.
            list3.add(key);
            list4.add(list1.get(i % list1.size()));  //<<< Change this!
        }
    }

Your code-link, edited with changes.