ArrayList is adding random values

Question

Okay,so i wanted to find the largest sub-string in a given string in java. So, i went ahead and wrote a recursive function for the same to identify and return the size of each sub string. My initial plan was to have all sizes of the sub-string added to Array list. I hen proposed to sort the array list in descending order and taking the top most value which would give me the size of the Largest sub-string. The problem is my ArrayList wen bonkers. Its not adding the values my function is returning but storing some other values.

My function is returning: 0 0 0 0 0 0 0 0 0 0 0 8 0 0 0 0 0 2 0 1

But what is stored is : 0 18 17 -1 -1 -1 -1 -1 11 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1

As you can this is totally different . I did figure out a solution but i want to know why ArrayList is not working as it should. Any insight will be greatly appreciated. Again i just want to know why the ArrayList is not working as it should.

package sush;
import java.util.ArrayList;
import java.util.Collections;

public class Paliandrome {

static int chk ( String s ,int x, int y,int count)
{
    String begins=s.charAt(x)+"";
    String end=s.charAt(y)+"";
    if(x==y && begins.equals(end))
    {
        System.out.println(count);
        return count+1;
    }
    if(x>y)
        return count;
    if(begins.equals(end))
        return chk(s,x+1,y-1,count+2);
    else
        return count=0;
}


public static void main(String[] args) 
{

    String sh = "aabaabaasdwaasddsaa";
    int x = 0 , y = 0;
    int count=0,high=0;
    ArrayList<Integer> arr = new ArrayList<Integer>();
    arr.clear();
    for(int i=0 ; i<sh.length() ; i++ )
    {
        x=i;
        y=sh.length()-1;
        count=0;
        int temp =chk(sh,x,y,count);
        System.out.println(temp);
        arr.add(temp);

    }     
    System.out.println(high+"\n"+"ArrayList contents :");
    for(int i= 0;i<arr.size();i++)
    {
        System.out.println(arr.indexOf(i));
    }
    Collections.sort(arr);
    Collections.reverse(arr);
    System.out.println(arr.indexOf(0));
}

}

k_g · Accepted Answer · 2015-01-10 06:12:22Z

2

You are using arr.indexOf(x) when you should be using arr.get(index).

List.indexOf(x) returns the first index of a given value in the list. -1 means that x isn't in the list.

On the other hand arr.get(index) returns the element at the given index.

answered Jan 10, 2015 at 6:12

k_g

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1 Comment

Shanmuga Shanker Over a year ago

your totally right.Totally noob mistake at my end , i'm just learning java. Thank you!

Vitruvie · Accepted Answer · 2015-01-10 06:16:03Z

0

The arraylist is working fine; the problem is that you're not using the right method to retrieve and print its elements:

    System.out.println(arr.indexOf(i));

ArrayList.indexOf(E) searches the array for E and returns the location of element E, or -1 if there is no such element. To retrieve elements from the array, as you want to do, use ArrayList.get(int) to retrieve the element at the specified position.

    System.out.println(arr.get(i));

Or, even better, use the ArrayList's iterator via an enhanced for loop:

for(int num : arr)
{
    System.out.println(num);
}

answered Jan 10, 2015 at 6:16

Vitruvie

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1 Comment

Shanmuga Shanker Over a year ago

Thanks for the tip!. I dont knw anything about iterator or enhanced for loop, Ill definitely look into it.

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