使用 ArrayList 和扫描仪从文本文件中打印特定数字

Question

I need to get a specific number out from a text file by typing a number using a scanner. The program needs to be able to add multiple numbers together.

Example If i type 1 then I would get the number 80. And after I type 2 then I would get the number 85 and then adding the two numbers together. Result 80 + 85 = 165.

My text file looks like this:

1
80

2
85

3
50

I am able to print all the numbers from my text file and getting it in to an ArrayList but I need to get a specific number printed out.

Answer 1

Instead of using Array list, use and store it in HashMap(key value pair) in java.

HashMap<Integer,Integer> map = new HashMap<Integer,Integer>();
map.put(1,80);
map.put(2,85);
// To retrieve the values 
map.get(2); // returns 85 

So that retrieval of values is easy and complexity O(1).

Answer 2

You can Read all the txt file data and stored it into the Map in Key value pair. Key will be Number index and Value will be actual number. Then fetch the keys from map and add their respective values. Code will look like:

public class NumberRead{
    public static String readFileAsString(String fileName)throws Exception 
    { 
        String data = ""; 
        data = new String(Files.readAllBytes(Paths.get(fileName))); 
        return data; 
    } 

    public static void main(String[] args) throws Exception {
        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
        String data = readFileAsString("-----Your Numbers.txt Path-----"); 
        String[] split = data.split("\\s+");
        for(int i=0;i<split.length;i++) {
            if(i%2==0) {
                map.put(Integer.parseInt(split[i]), Integer.parseInt(split[i+1]));
            }
        }
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter First Number Index");
        int first = sc.nextInt(); 
        System.out.println("Enter Secound Number Index");
        int second = sc.nextInt();

        if(map.containsKey(first)&&map.containsKey(second)) {
            System.out.println("Addition is: "+((map.get(first))+map.get(second)));
        } else {
            System.out.println("Indexes are not present");
        }
        sc.close();
    }
}

And your Numbers.txt file should be in following format:

1 80
2 85
3 50
4 95
5 75