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? — Ousmane D.
– Ousmane D., Commented Apr 2, 2018 at 12:40

Rahul · Accepted Answer · 2018-04-02 10:43:57Z

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 2, 2018 at 10:43

Rahul

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1 Comment

fps Over a year ago

No need to cast, either

Harsh Mehta · Accepted Answer · 2018-04-02 12:28:23Z

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 2, 2018 at 12:28

Harsh Mehta

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1 Comment

fps Over a year ago

Or better setOfString.removeIf(s -> s == null);, or with a method reference: setOfString.removeIf(Objects::isNull);

Pang · Accepted Answer · 2018-04-10 00:57:04Z

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);
        }
    }
}

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