how to remove specific object in an ArrayList while using a scanner in java

Question

I'm trying to remove a MemberPlayer(object) from my ArrayList(memberList) thorugh my input(scanner)

I have tried looking around google and Stack but can't seem to find anything that uses scanner.

    public void removeMember(){
    System.out.println("Which MemberPlayer are you looking for?:");
    System.out.print("Input first name: ");
    String fName = input.nextLine().toUpperCase();
    System.out.print("Input last name: ");
    String lName = input.nextLine().toUpperCase();

    for (MemberPlayer m: memberlist){
        if(m.getFirstName().contains(fName) && m.getLastName().contains(lName)) {
            System.out.println();
            System.out.println("This MemberPlayer exist:");
            System.out.println(fName + " " + lName);

            System.out.print("Do you want to remove this MemberPlayer?  [yes/no]");
            input.nextLine().toUpperCase();
            if (input.equals("Yes")) {
                memberlist.remove(); //I can't figure out how to write this line?
            }else{
                break;
            }
        }else {
            System.out.println();
            System.out.println("This MemberPlayer doesn't exist");
            System.out.println();
            break;
        }
    }
}

I read my memberlist from a file.txt with the following info: first name, last name, age and team.

ANDERS
ANDERSEN 23 1

BERT BERSEN 16 2

HANS HANSEN 25 1

TIM TIMSEN 20 2
MORTEN MORTENSEN 34 1

Did any of the answers work for you? If yes do consider upvoting/accepting one. [What should I do when someone answers my question?](https://stackoverflow.com/help/someone-answers) — Nicholas K, Feb 21 '19 at 14:04

score 0 · Answer 1 · edited Jun 20 '20 at 09:12

You need to use List#remove(), from the docs :

boolean remove(Object o)

Removes the first occurrence of the specified element from this list, if it is present (optional operation). If this list does not contain the element, it is unchanged. More formally, removes the element with the lowest index i such that (o==null ? get(i)==null : o.equals(get(i))) (if such an element exists). Returns true if this list contained the specified element (or equivalently, if this list changed as a result of the call).

Also, you don't need a for-loop here. Your method can be simplified to a much more OO approach :

public void removeMember() {
    System.out.println("Which MemberPlayer are you looking for?:");
    System.out.print("Input first name: ");
    String fName = input.nextLine().toUpperCase();
    System.out.print("Input last name: ");
    String lName = input.nextLine().toUpperCase();

    // create an object with input received
    MemberPlayer m = new MemberPlayer(fName, lName);

    // use contains of List
    if (memberlist.contains(m)) {
        memberlist.remove(m);
    } else {
        System.out.println("This MemberPlayer doesn't exist");
    }
}

Make sure you override the .equals() and .hashcode() methods in MemberPlayer.

I've been messing about with your solution and i can't seem to get it to work. I've added a construtor in MemberPlayer to handel the new object and i'm not quite sure by what you mean by overriding the .equals() and .hashcode() — FakeRune, Feb 17 '19 at 15:43
Which IDE are you using? You can auto-generate those methods. You can try a Google search regarding how to generate them. I'd be happy to help if you still are facing issues with it. — Nicholas K, Feb 17 '19 at 15:49
[Why should we override equals and hashcode](https://stackoverflow.com/questions/2265503/why-do-i-need-to-override-the-equals-and-hashcode-methods-in-java) might help you out further. — Nicholas K, Feb 17 '19 at 16:01

Fullstack Guy · Answer 2 · 2019-02-17T14:41:16.153

I recommend using an Iterator for this, as using the List.remove(Object o) can throw the ConcurrentModificationException as you are changing the state of the object while iterating.

So Iterator.remove() will be a safe bet. From the Java SE 1.8 docs:

Iterators allow the caller to remove elements from the underlying collection during the iteration with well-defined semantics.

So removing an object directly from the List using List.remove() will cause unpredictable iteration and throw ConcurrentModificationException while iterating it.

If you are not iterating then it is fine to use the List.remove(Object o) to remove the object from the List.

//Initializes the iterator, checks if next element is present by calling Iterator.hasNext()
for(Iterator<MemberPlayer> itr = memberList.iterator(); itr.hasNext(); ){
         m = itr.next(); //The current element of the List
         if(m.getFirstName().contains(fName) && m.getLastName().contains(lName)) {
            System.out.println();
            System.out.println("This MemberPlayer exist:");
            System.out.println(fName + " " + lName);

            System.out.print("Do you want to remove this MemberPlayer?  [yes/no]");
            input.nextLine().toUpperCase();
            if (input.equals("Yes")) {
                 itr.remove(); //Removes the current element if the condition is satisfied.
            }else{
                 break;
            }
         }else {
             System.out.println();
             System.out.println("This MemberPlayer doesn't exist");
             System.out.println();
             break;
         }
 }

LppEdd · Answer 3 · 2019-02-17T14:45:13.560

Remember that you cannot remove a Collection<T> element while you're iterating it using the for-each loop. In that case a ConcurrentModificationException might be thrown.

You need to explicitly use an Interator<T> or a ListIterator<T>, depending on the usecase.
A ListIterator allow also insertion of elements or setting of elements.

for (final Iterator<MemberPlayer> iterator = memberList.iterator(); iterator.hasNext();) {
   final MemberPlayer m = iterator.next();

   if (m.getFirstName().contains(fName) && m.getLastName().contains(lName)) {
      ...

      iterator.remove();
   }
}

score 0 · Accepted Answer · answered Feb 21 '19 at 16:10

this is what ended up working for me after some trial and error.

public void removeMember()throws FileNotFoundException {
    System.out.println("Which MemberPlayer are you looking to remove?:");
    System.out.print("Input first name: ");
    String fName1 = input.nextLine().toUpperCase();
    System.out.print("Input last name: ");
    String lName2 = input.nextLine().toUpperCase();

    for (MemberPlayer m : memberlist){

        if (m.getFirstName().equals(fName1) & m.getLastName().equals(lName2)) {
            System.out.println();
            memberlist.remove(m);
            System.out.println("You removed: "+m.getFirstName()+" "+m.getLastName());
            System.out.println();
            saveMember();
            break;
        } else {
            System.out.println();
            System.out.println("This MemberPlayer doesn't exist");
            System.out.println();
            break;
        }
    }
}

how to remove specific object in an ArrayList while using a scanner in java

4 Answers4