ArrayList input java

Question

I'm looking at the problem:

Write a program which reads a sequence of integers and displays them in ascending order.

I'm creating an ArrayList (which I am new to) and I want to populate with integers input from the command line. With an array I could use a for loop with:

for (int i =0; i < array.length; i++) {
    array[i] = scanner.nextInt();

but with an ArrayList of unbounded size I'm not sure how to process the input.

EDIT:

class SortNumbers {

    public static void main(String[] args) {
        List numbers = new ArrayList();
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter some numbers.");
        while (scanner.hasNextInt()) {
            int i = scanner.nextInt();
            numbers.add(i);
        }
    }
}

As soon as you're populating a list from scanner you whould probably iterate over scanner and just add to a list. — Piotr Gwiazda
– Piotr Gwiazda, Commented Aug 21, 2012 at 13:46
Please make sure you read this when asking homework questions (as most of your questions seem to be) meta.stackexchange.com/questions/10811/… — mjaggard
– mjaggard, Commented Aug 21, 2012 at 13:57
@Dave: the line: List numbers = new ArrayList(); will give rise to warnings based on raw types. Since you know (or assume) that the numbers will be integers you should define the list with type information, see my answer (or Piotr's). — posdef
– posdef, Commented Aug 21, 2012 at 14:38

posdef · Accepted Answer · 2012-08-21 13:48:09Z

9

The idea with using ArrayList is to avoid the deterministic iteration counts. Try something like this:

ArrayList<Integer> mylist = new ArrayList<Integer>();
while (sc.hasNextInt()) {
    int i = sc.nextInt();
    mylist.add(i);
}

answered Aug 21, 2012 at 13:48

posdef

6,58211 gold badges50 silver badges97 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

BLL27 Over a year ago

Thanks. How do I exit the while loop after entering a line of integers, ie not enter an infinite amount of integers? Im sure theres an easy way to do it,its just confusing me at the moment.

posdef Over a year ago

The sc.hasNextInt() should return false when the next token is not an integer (better put, when the next token cannot be parsed as an integer). See the documentation: docs.oracle.com/javase/7/docs/api/java/util/…

Piotr Gwiazda · Accepted Answer · 2012-08-21 13:47:57Z

5

I'd rather iterate over scanner and just add to a list:

List<Integer> list = new ArrayList<Integer>();
while(scanner.hasNextInt())
      list.add(scanner.nextInt());
}

then sort it.

answered Aug 21, 2012 at 13:47

Piotr Gwiazda

12.2k13 gold badges62 silver badges94 bronze badges

Comments

kosa · Accepted Answer · 2012-08-21 13:50:51Z

2

You need to use ArrayList add method

Example:

arraylist.add(nextVale);

You don't need to do for loop while using arraylist. As you add content, list size will increase automatically.

edited Aug 21, 2012 at 13:50

answered Aug 21, 2012 at 13:44

kosa

66.7k15 gold badges134 silver badges170 bronze badges

Comments

Liran Orevi · Accepted Answer · 2018-06-05 16:22:39Z

1

First if you have an ArrayList, you would not use [] to access/set the elements. That's for arrays, which is different from an ArrayList. You would use the add method,

Second, you need to sort the ArrayList. Check out Collections.sort in the API.

Finally, to iterate over a List, there are many constructs available. One of the most common is..

List<Integer> numbers = new ArrayList<Number>();

numbers.add(1);
numbers.add(2);
...

for (Integer number : numbers) {
   System.out.println(number);
}

edited Jun 5, 2018 at 16:22

Liran Orevi

4,9438 gold badges49 silver badges65 bronze badges

answered Aug 21, 2012 at 13:47

hvgotcodes

121k33 gold badges209 silver badges237 bronze badges

Comments

Alex K · Accepted Answer · 2012-08-21 14:08:32Z

0

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class sortArrayList {

    public static void main(string args[]) {
        List<Integer> arrList = new ArrayList<Integer>();
        while (scanner.hasNextIint()) {
            arrList.add(scanner.nextInt());
        }
        Collections.sort(arrList);
    }
}

edited Aug 21, 2012 at 14:08

Alex K

22.9k19 gold badges116 silver badges246 bronze badges

answered Aug 21, 2012 at 13:57

Bon Cyrus Macalindong

113 bronze badges

1 Comment

mjaggard Over a year ago

You need to not use back ticks when posting code over several lines. You also need to use a better standard of code - for example Java class names should have a capital letter to start.

The Photon · Accepted Answer · 2021-12-19 07:08:18Z

It is not that hard. Since you are using Array List, it is very easy!

import java.util.*;
class Arr{
public static void main(String args[]){
Scanner sc=new Scanner(System.in);//initializing scanner class
String cont="";//String to check whether the user wants to input anymore numbers or not
List<Double> n=new ArrayList<Double>();//List that will store our numbers
while(!(cont.equals("no"))){//taking continuous input

        System.out.println("Enter number:");
        n.add(sc.nextDouble());

        System.out.println("Do you want to continue?(type 'yes'/'no')");
        cont=sc.next();
    }
Collections.sort(n);//sorts your ArrayList
System.out.println("Sorted list:");
for (Double value : n) {//displaying sorted list
        System.out.println( value);
}
}
}

Georg Plaz · Accepted Answer · 2022-01-07 15:23:51Z

0

You can also use a for loop:

ArrayList<Integer> list = new ArrayList<Integer>();
for (int i = 0; i < 5; i++) {
    list.add(sc.nextInt());
}

edited Jan 7, 2022 at 15:23

Georg Plaz

6,0185 gold badges43 silver badges66 bronze badges

answered Jan 7, 2022 at 6:38

Abhishek

1491 silver badge6 bronze badges

Comments

Shankara K · Accepted Answer · 2024-05-19 17:12:30Z

-1

 List<Integer> list1 =  new ArrayList<>();
    try (Scanner sc = new Scanner(System.in)) {
        int n=sc.nextInt();

        for(int i=0;i<n;i++){
            list1.add(sc.nextInt());
        }
    }
    for(int n1:list1){
        System.out.print(n1+" ");
    }

edited May 19, 2024 at 17:12

answered Mar 16, 2024 at 16:56

Shankara K

13 bronze badges

2 Comments

Community Over a year ago

As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.

Abra Over a year ago

Answers that contain only code are generally considered poor quality. Also, the question states that the list of numbers be displayed in ascending order and I don't see how your code achieves that so I would argue that your answer is not correct. Nonetheless incorrect answers are still considered to be valid answers on this website. You can edit your answer and fix the code and also add some explanation as to how your code works, for example referencing the javadoc for the classes and methods in your code.

Collectives™ on Stack Overflow

ArrayList input java

8 Answers 8

2 Comments

Comments

Comments

Comments

1 Comment

Comments

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

8 Answers 8

2 Comments

Comments

Comments

Comments

1 Comment

Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related