creating array with elements determined by user/input

Question

trying to make an array, and want the elements to be however large the input will be. eventually this should take x amount of numbers, place in an array, and return the average. But first I need to figure out how placing the size of the elements in the array will be done.

import java.util.Scanner;
import java.util.ArrayList;
//needs to be an array

public class statsv2
{
   public static void main (String args[])
    {
        int[] a= new int[5];
        Scanner sc=new Scanner(System.in);
        System.out.println("Please enter numbers...");
        for(int j=0;j<5;j++)
        {
            a[j]=sc.nextInt();
        }
     }
}

So I essentially want the that '5'(which appears twice) to be however many times the user keeps entering new numbers

numbers are separated by a space or clicking 'enter' until the user enters a blank(empty) new line.. — tassin
– tassin, Commented Apr 18, 2013 at 1:27

Ray Stojonic · Accepted Answer · 2013-04-18 01:26:45Z

1

First of all, instead of j<5, use yourArray.length.

As to the array size, this cannot be done dynamically, you have three options:

1) Create an array large enough that the user won't overrun it, you'll have to do some extra checking in order to stop at the end of user input.

2) Use an ArrayList, which you can dynamically add to, then call 'toArray()' when the user is done entering data to extract an array for processing.

3) Skip the array altogether and use ArrayList to hold and process the input.

answered Apr 18, 2013 at 1:26

Ray Stojonic

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Community · Accepted Answer · 2017-05-23 11:44:52Z

Arrays can't really be dynamic in length. One of the things I would do would be to put all of your data into a structure like an array list, then when you get to the end of the input, convert that structure into an array.

Something like this would work.

import java.util.*;
import java.lang.Integer;

public class wut {
  public static void main(String[] args) { 
    ArrayList<String> list = new ArrayList<String>();
    Scanner scan = new Scanner(System.in);

    while (scan.hasNext())
    {   
      list.add(scan.next());
    }   

    //^D received.

    int[] a = new int[list.size()];
    for (int i = 0; i < list.size();i++)
    {   
      a[i] = Integer.parseInt(list.get(i));
    }   
    System.out.println(Arrays.toString(a));
  }   
}

output:

javac *.java

$ java wut
3
4
5
6
7
8
^D
[3, 4, 5, 6, 7, 8]

For the type of input you're looking for, look at the answer to this question: How to test for blank line with Java Scanner?

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