Java ArrayList of ArrayList Scanner UserInput

Question

I am trying to store user input into ArrayList of ArrayList.

ArrayList<ArrayList<Integer>> a = new ArrayList<ArrayList<Integer>>();

For example, storing it as [[1,2,3],[4,5],[6,1,8]]
Below is my code,

    Scanner input = new Scanner(System.in);
    System.out.println("Enter a set of numbers:");
    String line = input.nextLine();
    String[] numbers = line.split(" +");

    ArrayList<ArrayList<Integer>> a = new ArrayList<ArrayList<Integer>>();
    ArrayList<Integer> a1 = new ArrayList<Integer>();

    for(int i=0; i<numbers.length; i++) {
        a1.add(new Integer(numbers[i]));

    }
    a.add(a1);

But then when I types it in to terminal, it becomes [[1,2,3,4,5,6,1,8]].
Thank you in advance!

How did you input the numbers? I mean tell us where did you use +? — Aniket Kulkarni
– Aniket Kulkarni, Commented Oct 13, 2014 at 4:49
You created two ArrayList objects. What other output would you expect? — Voicu
– Voicu, Commented Oct 13, 2014 at 4:50
Please provide details about your input. you have coded only for one ArrayList. — Nishant Modi
– Nishant Modi, Commented Oct 13, 2014 at 4:50
basically i typed into the terminal by entering spacebar between numbers. eg 1 2 3 4 5 6 1 8 on one single line — user2875021
– user2875021, Commented Oct 13, 2014 at 4:53
How will you identify which is the first array list and which is second ? Put some separator. — SeeTheC
– SeeTheC, Commented Oct 13, 2014 at 4:54

Aniket Kulkarni · Accepted Answer · 2014-10-13 08:38:53Z

1

From above comments I am bit clear what do you want to do.

You entered 1 2 3 4 5 6 1 8 on terminal. In your program you used split on - so I am providing some guidelines to solve your problem.

First, split your input on - to make the separation of arrays

String[] numbersArray = line.split("-"); 
//e.g. input 1 2 3 + 4 5 6 + 1 8
//here you will get numbersArray as [1 2 3,4 5 6,1 8]
ArrayList<ArrayList<Integer>> a = new ArrayList<ArrayList<Integer>>();

Now, to separate individual elements of inner array use for loop

for(int i=0; i<numbersArray.length; i++) {

    String[] numbers= numbersArray[i].split(" "); //split on " "
    //here you will get [1,2,3] for first iteration and 2nd [4,5,6], last [1,8]

    ArrayList<Integer> a1 = new ArrayList<Integer>();
    for(int j=0; j<numbers.length; j++) {
        a1.add(new Integer(numbers[j]));
        //here adding inner array list elements

    }
    //add to main array list 
    a.add(a1);
}

edited Oct 13, 2014 at 8:38

answered Oct 13, 2014 at 5:08

Aniket Kulkarni

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3 Comments

user2875021 Over a year ago

however, when i am trying using your method, entering to the terminal like 1 2 3 + 4 5 6 + 1 8 i got a Runtime Error with NumberFormatException. not quite sure why thou.

user2875021 Over a year ago

I have figured it out. Instead of using ("+"), I have used ("-") and works like a charm.

Aniket Kulkarni Over a year ago

@user2875021 : Fine. It's GOOD to see you have solved the problem. SO is always there to help you.

SeeTheC · Accepted Answer · 2014-10-13 04:58:15Z

1

Try this type of i/p and below code .

i/p : 1 2 3-4 5-6 1 8

String[] list= line.split("-");

ArrayList<ArrayList<Integer>> a = new ArrayList<ArrayList<Integer>>();
for(int i=0; i<list.length; i++) {

        String[] number= line.split(" ");
        ArrayList<Integer> a1 = new ArrayList<Integer>();
        for(int i=0; i<numbers.length; i++) {
            a1.add(new Integer(numbers[i]));

        }
        if(a1.length>0)
           a.add(a1);
}

answered Oct 13, 2014 at 4:58

SeeTheC

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Comments

gaurav aggarwal · Accepted Answer · 2014-10-13 04:56:46Z

0

I think it's due to the wrong input you are trying to enter on console, because when I hard code the ideal input to your ArrayList it prints the result as you expected. Here is the sample code that I wrote:

private static void doPrint(){
    List<List<Integer>> sample=new ArrayList<List<Integer>>();
    ArrayList<Integer> a1 = new ArrayList<Integer>();
    a1.add(12);
    a1.add(23);
    ArrayList<Integer> a2 = new ArrayList<Integer>();
    a2.add(22);
    a2.add(28);
    sample.add(a1);
    sample.add(a2);

    System.out.println(sample);
}

and here is the output:

[[12, 23], [22, 28]]

answered Oct 13, 2014 at 4:56

gaurav aggarwal

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Comments

Ruchira Gayan Ranaweera · Accepted Answer · 2014-10-13 04:56:52Z

0

The way you are trying to use, will not work since you add all elements to inner list.

You can try some thing like following. You needs to create following arrays.

public static void main(String[] args) {
    ArrayList<ArrayList<Integer>> a = new ArrayList<>();
    int[] arr1={1,2,3}; // you need to create these arrays
    int[] arr2={4,5};
    int[] arr3={6,1,8};
    a.add(getList(arr1));
    a.add(getList(arr2));
    a.add(getList(arr3));
    System.out.println(a);
}

public static ArrayList<Integer> getList(int[] arr){
    ArrayList<Integer> list = new ArrayList<>();
    for (int anArr : arr) {
        list.add(anArr);
    }
    return list;
}

answered Oct 13, 2014 at 4:56

Ruchira Gayan Ranaweera

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Comments

Qadir Hussain · Accepted Answer · 2014-10-13 04:59:03Z

0

You are adding only one list to a that's why it seems like one element inside list a. If you want to have multiple elements inside list a then use like this.

for(int i=0; i<numbers.length; i++) {
        a1.add(new Integer(numbers[i]));
}
a.add(a1);
a.add(a1);

Output: As per input taken in your question

[[1,2,3,4,5,6,1,8], [1,2,3,4,5,6,1,8]]

answered Oct 13, 2014 at 4:59

Qadir Hussain

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