从arraylist java中删除项目

Question

I am trying to compare weather an item is contained within the arrayList and if it is then remove it. Im not sure weather I have to implement my own equals method or not, this is my code but it isn't working to remove the correct item.

  public boolean removeItem(Item item) {

    for(int i = 0; i < items.size(); i++) {

        if (items.get(i).equals(item)) {
            items.remove(item);
            return true;
        } 


    }
    return false;
}

Answer 1

You can safely remove items from a Collection using Iterator

public boolean removeItem(Item item) {    
  Iterator<Item> it = items.iterator();
  while (it.hasNext()) {
     Item i = it.next();
     if(i.equals(item)) {
       it.remove();
       // remove next line if you want to remove all occurrences `item`
       return true; 
     }      
  }
  return false;
}

You could also just call

items.remove(item);

Answer 2

ArrayList#remove(Object) will do exactly that! But this works only if you have overridden the equals method of Item . If You want to remove all elements, will need a loop:

public int remove(Item item) {
    int i = 0;

    while(list.remove(item)) {
        i++;
    }

    return i;
}

this will return the amount of items that have been removed

Removes the first occurrence of the specified element from this list, if it is present. If the 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).

Answer 3

I think you want contains not equals`. You don't even need to loop it. That's the magic of the method.

public boolean removeItem(Item item) {

    if (items.contains(item)){
        items.remove(item);
    }
    return false;  // I have no idea why you want to return false.
                   // I'll just leave it there
}

Answer 4

Yes you have to override equals in your class.Compare every single attribute and when one of them dont equals the other, then return false. If you use eclipse for example, you can let it create the equals method for your class.