CODEWITHSUNDEEP
javaarraylist
user3242607
user3242607

Reputation: 219

How do i return an ArrayList<String> from a method?

Here is my first method. I have a file that I added its contents to an ArrayList. I can print that just fine but I need to create a method that adds line numbers to the beginning of each String. I can do that outside the method but i'm having problems creating a method that returns an arrayList so i can use the updated arrayList in other methods and then I need to display the updated ArrayList. Here is my code.

My output for the first method should be 1 bird 2 cat etc...

My output for the second method should return the elements in the ArrayList in reverse order. 2 cat 1 bird etc...

import java.util.*;
import java.io.*;




public class List 
{
public static void main(String[] args) throws IOException
{
    int line =1;
    ArrayList<String> textArray = new ArrayList<String>();
    ArrayList<String> newArray = new ArrayList<String>();
    File f = new File("src/List.txt");


    Scanner sc = new Scanner(f);
    int num = 1;
    while(sc.hasNext())
    {


        textArray.add(sc.nextLine());


    }


    numbered(textArray);
    reverseOrder(textArray);

}

public static ArrayList<String> numbered(ArrayList<String> textArray)
{
    ArrayList<String> results = new ArrayList<String>(textArray.size());
    String s;
    int num = 1;
    for (String r : results)
    {
        r = num + " " + results;
        num++;
    }

     return results;
}

public static ArrayList<String> reverseOrder(ArrayList<String> textArray)
{
    ArrayList<String> results = new ArrayList<String>(textArray.size());
    String s;
    int num = 1;
    for (String r : results)
    {

    }

     return results;
}

Upvotes: 0

Views: 103

Answers (3)

AhabLives
AhabLives

Reputation: 1468

Have not tested this but it should work. As you can see pretty straight forward. Best of Luck and happy coding.

public ArrayList<String> numList(ArrayList<String> originalArrayList)
{
    ArrayList<String> newNumberedList = new ArrayList<String>();

    for(int i = 0;i< originalArrayList.size(); i++){

        int newi = i+1;
        newNumberedList.add(newi+". "+originalArrayList.get(i));

    }

    return newNumberedList ;
}

Upvotes: 1

Paco Lagunas
Paco Lagunas

Reputation: 330

You are returning your arrays correctly, the problem is that you are creating new Objects inside your methods, instead of using the ones you receive as parameters

ArrayList<String> results = new ArrayList<String>(textArray.size());

So you are iterating empty arrays. Inside your for loop, you could just iterate the received ArrayList

for (String r : textArray)

Also, your results array is always empty, you should add new elements like this:

results.add(r);

This may work:

public static ArrayList<String> numbered(ArrayList<String> textArray)
{
    ArrayList<String> results = new ArrayList<String>(textArray.size());
    String s;
    int num = 1;
    for (String r : textArray)
    {
        r = num + " " + results;
        num++;
        results.add(r);
    }
    return results;
}

Upvotes: 1

ne1410s
ne1410s

Reputation: 7082

You are instantiating the 'results' arraylist, and iterating it. You need to iterate the textArray list for starters and call results.add("text");

Upvotes: 0

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