Which Data Structure would be more suitable for the following task in Java?

Question

Every 5 minutes, within the 20th minute cycle, I need to retrieve the data. Currently, I'm using the map data structure.

Is there a better data structure? Every time I read and set the data, I have to write to the file to prevent program restart and data loss.

For example, if the initial data in the map is:

{-1:"result1",-2:"result2",-3:"result3",-4:"result4"}

I want to get the last -4 period's value which is "result4", and set the new value "result5", so that the updated map will be:

{-1:"result5",-2:"result1",-3:"result2",-4:"result3"}

And again, I want to get the last -4 period's value which is "result3", and set the new value "result6", so the map will be:

{-1:"result6",-2:"result5",-3:"result1",-4:"result2"}

The code:

private static String getAndSaveValue(int a) { 
    //read the map from file
    HashMap<Long,String> resultMap=getMapFromFile();
    String  value=resultMap.get(-4L);

    for (Long i = 4L; i >= 2; i--){
        resultMap.put(Long.parseLong(String.valueOf(i - 2 * i)),resultMap.get(1 - i));
    }
    resultMap.put(-1L,"result" + a);
    //save the map to file
    saveMapToFile(resultMap);

    return value;
}

Answer 1

Based on your requirement, I think LinkedList data structure will be suitable for your requirement:

public class Test {
    public static void main(String[] args) {        
        LinkedList<String> ls=new LinkedList<String>();
        ls.push("result4");
        ls.push("result3");
        ls.push("result2");
        ls.push("result1");
        System.out.println(ls);
        ls.push("result5"); //pushing new value
        System.out.println("Last value:"+ls.pollLast()); //this will return `result4`
        System.out.println(ls);
        ls.push("result6"); //pushing new value
        System.out.println("Last value:"+ls.pollLast());  // this will give you `result3`
        System.out.println(ls);
    }
}

Output:

[result1, result2, result3, result4]
Last value:result4
[result5, result1, result2, result3]
Last value:result3  
[result6, result5, result1, result2]