使用for循环从ArrayList中删除特定对象

Question

I am trying to delete one object from an ArrayList, but after iterating through the list with the for loop i'm stuck at what to do next. nameInput is a lowercase string from the user.

If i run this it prints the object from arr list equal to the input from nameInput. But I cannot understand how to go from printing that object to deleting it?

I'm sure this is a stupid question but the 50+ answers i have read and tried all seem to fail me (or more likely I fail to understand them). I have tried the list.remove and removeIf.

private ArrayList<Arr> arr = new ArrayList<>();

private void removeItem() {
    for (Object arr : arr) {
        if (((Arr) arr).getName().equals(nameInput())) {
            System.out.println(arr);        
            break;
        } else {
            System.out.println("Error");
        }
    }
}

Answer 1

Using for loop

List<Arr> arr = new ArrayList<>();

for (Arr item : arr) {
    if (item.getName().equals(nameInput())) {
        arr.remove(item);
        break;
    }
}

If not call break after remove element, you get ConcurrentElementException

Note from @Aomine : you have to implement correct Arr.equals() method.

---

Using Iterator

List<Arr> arr = new ArrayList<>();
Iterator<Arr> it = arr.iterator();

while (it.hasNext()) {
    Arr items = it.next();

    if (item.getName().equals(nameInput())) {
        it.remove();
        break;  // you can continue iterating and remove another item
    }

}

---

Using Streams

List<Arr> arr = new ArrayList<>();
arr.removeIf(item -> item.getName().equals(nameInput()));

Remove all items that match given condition

---

This is not good to remove element from ArrayList . In case you know that you have to remove element from the middle of the List , do use LinkedList .

Answer 2

You are trying to remove an item while you are traversing/iterating the list in the for loop. You cannot remove an item from the list iterating it in a for loop. Use an Iterator instead and invoke arr.remove() .

Answer 3

If you use Java 8 you could do

private void removeItem() {
    arr.removeIf(t -> t.getName().equals(nameInput));
}

Note that this will remove all objects with name equal to nameInput

Also you should change your declaration of arr to

List<Arr> arr = new ArrayList<>();

Answer 4

A couple of things here...

1. The loop variable receiver type should ideally be Arr instead of Object as the list contains Arr objects. This also means you no longer need the cast you're performing.
2. You could remove the item via remove(Object o) but this requires overriding equals and hashcode based on name only. Another option is via an iterator but this would mean changing your code completely. Thus, to keep it as close to your code as possible you can use a for loop; get the index which the object is located and then remove.

Thus, you can do:

for(int i = 0; i < arr.size(); i++){
    if (arr.get(i).getName().equals(nameInput)) {
          Arr obj = arr.remove(i); // remove the item by index     
          System.out.println(obj);  // print the object             
          break;  // terminate the loop iteration
     }
}