Compare two array-list element and get un-common element

Question

I have done something like this :

public class MainActivity extends AppCompatActivity {

    ArrayList<String> al = new ArrayList<String>();
    ArrayList<String> a2 = new ArrayList<String>();


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        al.add("C");
        al.add("A");
        al.add("E");
        al.add("B");
        al.add("D");
        al.add("F");

        a2.add("C");
        a2.add("C");
        a2.add("E");
        a2.add("B");
        a2.add("D");
        a2.add("F");


        for (int i = 0; i < al.size(); i++) {
            for (int j = 0; j < a2.size(); j++) {

                if (al.get(i).equals(a2.get(j))) {
                    a2.remove(j);
                    Log.e("array 2 ", a2.toString());
                    break;
                }

            }
        }
     } 
  }

-- But my output is like this :

[C, E, B, D, F]
[C, B, D, F]
[C, D, F]
[C, F]
[C]

-- i am having same elements in arraylist 2, then also i am getting 'C', it should be null .i.e zero un-common value.

al.removeAll(a2) removes the common items between al and a2. Read more here — Blackbelt
– Blackbelt, Commented Mar 29, 2016 at 10:06

HendraWD · Accepted Answer · 2016-03-29 10:15:11Z

3

You are messing with the index when you remove the a2 items directly inside for loop. Refer to my solution below

        ArrayList<String> al = new ArrayList<>();
        ArrayList<String> a2 = new ArrayList<>();
        al.add("C");
        al.add("A");
        al.add("E");
        al.add("B");
        al.add("D");
        al.add("F");

        a2.add("C");
        a2.add("C");
        a2.add("E");
        a2.add("B");
        a2.add("D");
        a2.add("F");

        ArrayList<String> tempToDelete = new ArrayList<>();

        for (int i = 0; i < al.size(); i++) {
            for (int j = 0; j < a2.size(); j++) {
                if (al.get(i).equals(a2.get(j))) {
                    tempToDelete.add(a2.get(j));
                    break;
                }

            }
        }

        a2.removeAll(tempToDelete);

for shorter method, you can just do this:

a2.removeAll(al);

answered Mar 29, 2016 at 10:15

HendraWD

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1 Comment

MohanRaj S Over a year ago

thank you so much, I tried both method, First working fine for the object arraylist. your solution saved my time cheers :)

Abhishek Patel · Accepted Answer · 2016-03-29 10:20:59Z

1

Try This it will help you

     ArrayList<String> al = new ArrayList<String>();
     ArrayList<String> a2 = new ArrayList<String>();

    al.add("C");
    al.add("A");
    al.add("E");
    al.add("B");
    al.add("D");
    al.add("F");

    a2.add("C");
    a2.add("C");
    a2.add("E");
    a2.add("B");
    a2.add("D");
    a2.add("F");

   Integer a = null;
 for (int i=0; i<a1.size(); i++)
  {
    a = a1.get(i);

    if (a2.contains(a)
{
    a2.remove(a);
    a1.remove(a);
    i--;
 }
 }

ArrayList<String> finaldata = new ArrayList<String>();
finaldata.addAll(a1);
finaldata.addAll(a2);
// finaldata = { A}

edited Mar 29, 2016 at 10:20

answered Mar 29, 2016 at 10:06

Abhishek Patel

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1 Comment

N J Over a year ago

final is keyword in Java

Parsania Hardik · Accepted Answer · 2016-03-29 10:45:45Z

0

Just replace break; with this:

j = -1;

code:

 for (int i = 0; i < al.size(); i++) {
        for (int j = 0; j < a2.size(); j++) {

            if (al.get(i).equals(a2.get(j))) {
                a2.remove(j);
                Log.e("array 2 ", a2.toString());
                j = -1;

            }

        }
    }

answered Mar 29, 2016 at 10:45

Parsania Hardik

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Comments

Community · Accepted Answer · 2017-05-23 12:17:23Z

0

I recommend you to use Set's instead of ArrayList. You can find some info here.

Also, here you can read some examples of using java Set in set operations in this stackoverflow answer.

edited May 23, 2017 at 12:17

CommunityBot

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answered Mar 29, 2016 at 10:18

juliocb92

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