Remove All null from ArrayList Using Iterator's remove() method

Question

I am new for Java . I was just looking for the Iterator in Collection Framework. but now I want to remove all null from ArrayList by using Iterator's remove() method .so tried following code but I am not getting expected output as I want a list without any null values . please explain someone Thank you.

here is my code

package setinterface;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

public class InternalWorkingOfArrayList {

    public static void main(String[] args) {

        List<String> setOfString = new ArrayList<String>();
        setOfString.add("A");
        setOfString.add("B");
        setOfString.add("C");
        setOfString.add("B");
        setOfString.add(null);
        setOfString.add("A");
        setOfString.add(null);


        Iterator<String> iterator = setOfString.iterator();
        while (iterator.hasNext()) {
            String string = (String) iterator.next();
            if (null==string) {
                iterator.remove();
                break;
            }   
        }
        for (String string1 : setOfString) {
            System.out.println(string1);
        }
    }
}

Possible duplicate of [How to remove all null elements from a ArrayList or String Array?](https://stackoverflow.com/questions/4819635/how-to-remove-all-null-elements-from-a-arraylist-or-string-array) — Ousmane D., Apr 02 '18 at 12:40

score 5 · Answer 1 · answered Apr 02 '18 at 10:43

5

Why are you breaking the loop?? Remove break statement from your code.

while (iterator.hasNext()) {
            String string = (String) iterator.next();
            if (null==string) {
                iterator.remove();
                //break;
            }   
        }

answered Apr 02 '18 at 10:43

Rahul

3,479
3
16
28

No need to cast, either – fps Apr 03 '18 at 21:17

score 2 · Answer 2 · edited Apr 10 '18 at 00:57

What you are doing wrong here is that you are directly trying to cast your element into string. This would give you an exception for a null element.

This is what you could do precisely.

package setinterface;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

public class InternalWorkingOfArrayList {

    public static void main(String[] args) {

        List<String> setOfString = new ArrayList<String>();
        setOfString.add("A");
        setOfString.add("B");
        setOfString.add("C");
        setOfString.add("B");
        setOfString.add(null);
        setOfString.add("A");
        setOfString.add(null);


        Iterator<String> iterator = setOfString.iterator();
        while (iterator.hasNext()) {
            if (null==iterator.next()) {
                iterator.remove();
            }   
        }
        for (String string1 : setOfString) {
            System.out.println(string1);
        }
    }
}

score 2 · Answer 3 · answered Apr 02 '18 at 12:28

2

Using Java-8 features, you can achieve it with a single line of code in following way...

setOfString.removeAll(Collections.singleton(null));

And then print the output:

System.out.println(setOfString); //output would be: [A, B, C, B, A]

answered Apr 02 '18 at 12:28

Harsh Mehta

571
3
16

Or better `setOfString.removeIf(s -> s == null);`, or with a method reference: `setOfString.removeIf(Objects::isNull);` – fps Apr 03 '18 at 21:18

Remove All null from ArrayList Using Iterator's remove() method

3 Answers3