Is there a way that I can compare an array and an arraylist?

Question

Is there a way that I can compare an array and an arraylist like

if (array[0]==arraylist[0])

I am working on this problem:

String[] s= {"a","a","b","b","b","c"};
ArrayList<String> list = new ArrayList<String>();
list.add("a");
list.add("b");
list.add("c");
// create a new arraylist that stores the frequency of each character. 
// For example, "a" appears twice in s, so newArrayList[0]=2; "b" appears 
// three times, so newArrayList[1]=3, and so on.

My idea is using a loop to scan through the string array and every time when a letter in it equals the letter in list, int count++. But I dont know how to compare things in an array and things in an arraylist.

You are a bit vague about what the comparison should be. Is it just an equals? Or to you want to know something more specific. — redge
– redge, Commented Apr 5, 2015 at 2:53
You can't even compare two arrays that way (at least not meaningfully). — Hot Licks
– Hot Licks, Commented Apr 5, 2015 at 2:59
Why are you mixing arrays and array lists to begin with? It's certainly possible to compare the two together, but one would generally avoid mixing and matching their data structures in this manner. — Makoto
– Makoto, Commented Apr 5, 2015 at 3:19
Do you have to use an arraylist to store the frequency? Hashmap would be much better for this purpose — Mshnik
– Mshnik, Commented Apr 5, 2015 at 3:22

Evgeniy Dorofeev · Accepted Answer · 2015-04-05 03:44:07Z

5

Shortest way is this

Arrays.asList(arr).equals(list)

answered Apr 5, 2015 at 3:44

Evgeniy Dorofeev

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1 Comment

Bohemian Over a year ago

And not far off the fastest too

mattm · Accepted Answer · 2015-04-05 02:54:00Z

1

Yes, you can iterate through the array and arraylist and compare elements. ArrayList elements are accessed with .get(index). And if you are comparing Objects (non-primitives), you need to use the .equals() method, not ==.

if(array[i].equals(arrayList.get(i) ) )

answered Apr 5, 2015 at 2:54

mattm

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Comments

Tom · Accepted Answer · 2015-04-05 03:44:47Z

import java.util.ArrayList;

public class ArrayAndArrayListElementsComparison {
    public static int compareArrayAndArrayListElements(String[] array, ArrayList<String> arraylist) {
        int count = 0;
        for (String s : array) {
            if (arraylist.contains(s)) {
                count++;
            }
        }
        return count;
    }

    public static void main(String[] args) {
        String[] array = {"a", "a", "b", "b", "b", "c"};
        ArrayList<String> arraylist = new ArrayList<String>();
        System.out.println("");
        arraylist.add("a");
        arraylist.add("b");
        arraylist.add("c");

        if (!arraylist.isEmpty() && array.length > 0) {
            if (compareArrayAndArrayListElements(array, arraylist) == array.length) {
                System.out.println("ArrayList contains all the elements in Array");
            } else if (compareArrayAndArrayListElements(array, arraylist) > 0) {
                System.out.println("ArrayList contains only few elements in Array");
            } else {
                System.out.println("ArrayList contains none of the elements in Array");
            }
        } else {
            System.out.println("Either ArrayList or Array is Empty.");
        }
    }
}

Nam Tran · Accepted Answer · 2015-04-05 03:05:21Z

-1

You try

if (array[0].equals(arraylist[0]))

As in java comparisons string should use equals(). It's not like javascript.

edited Apr 5, 2015 at 3:05

answered Apr 5, 2015 at 2:56

Nam Tran

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1 Comment

dnault Over a year ago

arraylist[0] isn't going to work... Do you mean arraylist.get(0)?

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