如何显示从自定义 OrderedLinkedList 类的列表中删除了哪些元素

Question

我正在实现一个带有嵌套有序ListNode类的自定义有序LinkedList类。 一切正常，但我正在尝试通过访问已删除的元素来扩展它。

这不是必需的，但我很好奇这将如何工作，因为我只能使用我被指示创建的方法，即boolean add()、boolean remove()和clear()。

我还在跟踪每个修改，每次成功添加、删除或调用clear()都会增加。我可以简单地创建另一个OrderedLinkedList，并将已删除的元素添加到其中，但我觉得我正在添加不必要的修改计数。

同样，这部分只是为了好玩，不是必需的。我觉得这将使我对创建自定义类有更深入的了解。

我将展示删除和主要方法。无法更改删除方法签名。

public boolean remove(Comparable obj) {
    for(OrderedListNode element = head.next; element != tail; element = element.next) {
    if(obj.equals(element.dataItem)) { //if element being removed is at the cursor
        OrderedListNode previousNode = element.before;
        OrderedListNode nextNode = element.next;
        nextNode.before = previousNode; //places next element that's after before to the element after current element [prev -> current -> next]
        previousNode.next = nextNode; //places prev of next element to the element before current
        element.dataItem = (Comparable)NOT_FOUND; //removed element is now null
        modCount++; //another modification
        theSize--; //reduce the size by 1
        return true; //if remove is successful
    }
}
return false; //otherwise, not successful removal
}

主要方法：

public static void main(String[] args) {
   OrderedLinkedList list = new OrderedLinkedList();
   OrderedLinkedList removedList = new OrderedLinkedList();
   modCount = 0;
   list.add("Dog");
   list.add("Bird");
   list.add("dog");
   list.add("bird");
   list.add("Cat");
   System.out.println("Before removal of element");
   System.out.println(list);
   list.remove("Dog");
   removedList.add("Dog"); //not what I'm wanting to do
   System.out.println("Removed " + removedList);
   System.out.println("After removal of element");
   System.out.println(list);
   System.out.println("Total modifications = " + modCount);
   System.out.println();
}

输出：

Before removal of element
Bird, Cat, Dog, bird, dog
Removed Dog //not actually accessing the element originally removed. just printing a new list
After removal of element
Bird, Cat, bird, dog
Total modifications = 7 //unnecessary modification due to additional add

Answer 1

如果您只想存储已删除的元素而不增加修改计数，则可以使用 ArrayList 并将已删除的元素放入其中。这样，您的修改计数就不会受到影响。

Answer 2

可以通过实现其他 pop 方法来存储已删除的值。返回类型应为 Comparable ，当找到要删除的对象时，将其存储在临时对象中并返回该对象，而不是返回布尔值true。如果未找到对象，只需返回 null。

如果找到要删除的 Comparable 对象，该方法将返回该对象，以便您可以存储它。如果没有，将返回 null，以便您可以使用 if-check for pop 方法来获取删除是否成功。

这是我刚刚为您编写的示例方法;

示例弹出方法

public Comparable pop(Comparable obj) {
    for (OrderedListNode element = head.next; element != tail; element = element.next) {
        Comparable temp = null;     // declaration of the temporary object
        if (obj.equals(element.dataItem)) { // if element being removed is
                                            // at the cursor
            temp = obj;                     // store obj in temp
            OrderedListNode previousNode = element.before;
            OrderedListNode nextNode = element.next;
            nextNode.before = previousNode; // places next element that's
                                            // after before to the element
                                            // after current element [prev
                                            // -> current -> next]
            previousNode.next = nextNode;   // places prev of next element to
                                            // the element before current
            element.dataItem = (Comparable) NOT_FOUND;  // removed element is
                                                        // now null
            modCount++; // another modification
            theSize--; // reduce the size by 1
            return temp; // if remove is successful
        }
    }
    return null; // otherwise, not successful removal
}

测试演示

你的测试代码应该是这样的;

public static void main(String[] args) {
    OrderedLinkedList list = new OrderedLinkedList();
    OrderedLinkedList removedList = new OrderedLinkedList();
    modCount = 0;
    list.add("Dog");
    list.add("Bird");
    list.add("dog");
    list.add("bird");
    list.add("Cat");
    System.out.println("Before removal of element");
    System.out.println(list);
    // list.remove("Dog"); // not needed anymore
    // removedList.add("Dog"); //not what I'm wanting to do
    // pop returns the removed object
    removedList.add(list.pop("Dog"));
    System.out.println("Removed " + removedList);
    System.out.println("After removal of element");
    System.out.println(list);
    System.out.println("Total modifications = " + modCount);
    System.out.println();
}