CODEWITHSUNDEEP
javaarraylist
Akhila
Akhila

Reputation: 609

How to read input into ArrayList?

public static void main(String[] args) 
{
        Scanner sc = new Scanner(System.in);
        int t = sc.nextInt();
        while (t-->0) 
        {
            int n=sc.nextInt();
            ArrayList <Integer> arr=new ArrayList<Integer>();
            for(int i=0; i<n; i++) 
            {
                arr.add(sc.nextInt());
            }
            System.out.println(arr);
       }
}

I already know the size of the ArrayList. I also saw other questions, but they read using the hasNext(), when the size is unknown. How do I do it this way, when the array size is previously known? I just wanted to use inbuilt functions like rotate() and hence I want to create this. But this just doesn't work. it adds nothing to the list. I even tried reading as an array and using Collections.addAll to put to a new ArrayList, but that also isn't working. When I tried to convert after reading as an array to ArrayList that is giving me other errors. I also tried reading as an integer variable and adding into the list without directly inserting. That gives me just one element inserted. I don't know why.

Edit: It was an error in inputting from my part. It's solved.

Upvotes: 0

Views: 101

Answers (1)

solid.py
solid.py

Reputation: 2812

By using scan.nextLine() you can get multiple numbers in the same line, instead of inputting them one-by-one by calling, scan.nextInt(). This is showcased in the code below:

import java.util.Arrays;
import java.util.Scanner;

public class Main {

    public static Integer[] convertToIntArray(String[] arr) {
        int index = 0;
        Integer[] numbers = new Integer[arr.length];

        for (int i = 0; i < arr.length; ++i) {
            try {
                numbers[index] = Integer.parseInt(arr[i]);
                ++index;
            } catch (NumberFormatException nfe) {
                // This part skips invalid input, which is not a number.
                // by not saving the skipped element to the array.
            }
        }
        return numbers;
    }

    public static void main(String[] args) {
        // Get the line containing numbers from the user.
        System.out.println("Input numbers: ");
        Scanner scan = new Scanner(System.in);
        String s = scan.nextLine();
        // Split sentence into words.
        String[] arr = s.split("\\W+");
        // Convert string array of numbers to int.
        Integer[] numbers = convertToIntArray(arr);
        System.out.println(Arrays.toString(numbers));
    }
}

When run with an input of 10 numbers this outputs:

Input numbers: 
1 2 3 4 5 6 7 8 9 10
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Upvotes: 1

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