Java中AbstractSequentialList clear()方法的示例

在Java中，AbstractSequentialList是一个抽象类，它实现了List接口并提供了对于基于链表结构的列表操作的默认实现。AbstractSequentialList中的clear()方法是用来清空列表中的所有元素的方法。在本文中，我们将学习如何使用Java中AbstractSequentialList的clear()方法。

AbstractSequentialList clear()方法的定义

在Java中，AbstractSequentialList的clear()方法的定义如下：

public void clear() {
    ...
}

AbstractSequentialList clear()方法的实现

在AbstractSequentialList类中，由于它是一个抽象类，因此我们不能创建一个AbstractSequentialList对象的实例。所以在这里，我们需要先创建一个子类，然后再在子类中重写clear()方法的实现。以下是一个名为MyList的子类，我们将在这个子类中重写AbstractSequentialList类的clear()方法的实现：

import java.util.AbstractSequentialList;
import java.util.ListIterator;

public class MyList<E> extends AbstractSequentialList<E> {
    private Node<E> head;
    private Node<E> tail;
    private int size;

    public MyList() {
        head = new Node<>(null, null, null);
        tail = new Node<>(null, head, null);
        head.next = tail;
    }

    @Override
    public ListIterator<E> listIterator(int index) {
        return new MyListIterator<>(index);
    }

    @Override
    public int size() {
        return size;
    }

    private static class Node<E> {
        E element;
        Node<E> prev;
        Node<E> next;

        Node(E element, Node<E> prev, Node<E> next) {
            this.element = element;
            this.prev = prev;
            this.next = next;
        }
    }

    private class MyListIterator<E> implements ListIterator<E> {
        private Node<E> lastReturned = head;
        private Node<E> next;
        private int nextIndex;

        MyListIterator(int index) {
            next = (Node<E>) MyList.this.get(index);
            nextIndex = index;
        }

        @Override
        public boolean hasNext() {
            return nextIndex < size;
        }

        @Override
        public E next() {
            if (!hasNext())
                throw new IndexOutOfBoundsException("index out of bounds");

            lastReturned = next;
            next = next.next;
            nextIndex++;

            return lastReturned.element;
        }

        @Override
        public void remove() {
            if (lastReturned == head)
                throw new IllegalStateException("illegal operation");

            Node<E> lastPrevious = lastReturned.prev;
            lastPrevious.next = next;
            next.prev = lastPrevious;
            size--;
            lastReturned = head;
        }

        @Override
        public boolean hasPrevious() {
            return nextIndex > 0;
        }

        @Override
        public E previous() {
            if (!hasPrevious())
                throw new IndexOutOfBoundsException("index out of bounds");

            nextIndex--;
            next = lastReturned;
            lastReturned = lastReturned.prev;

            return next.element;
        }

        @Override
        public int nextIndex() {
            return nextIndex;
        }

        @Override
        public int previousIndex() {
            return nextIndex - 1;
        }

        @Override
        public void set(E e) {
            lastReturned.element = e;
        }

        @Override
        public void add(E e) {
            Node<E> newNode = new Node<>(e, lastReturned, lastReturned.next);
            lastReturned.next.prev = newNode;
            lastReturned.next = newNode;
            size++;
            nextIndex++;
            lastReturned = head;
        }
    }

    @Override
    public void clear() {
        for(Node<E> x = head.next; x != tail; ) {
            Node<E> next = x.next;
            x.element = null;
            x.prev = null;
            x.next = null;
            x = next;
        }
        head.next = tail;
        tail.prev = head;
        size = 0;
    }
}

AbstractSequentialList clear()方法的使用

现在我们已经实现了AbstractSequentialList类的子类MyList，我们可以在这个子类中调用AbstractSequentialList的clear()方法来清空列表中的所有元素。以下是如何使用这个方法的示例：

import java.util.ListIterator;

public class Main {
    public static void main(String[] args){
        MyList<Integer> list = new MyList<>();
        list.add(1);
        list.add(2);
        list.add(3);

        // 打印列表原来的元素
        ListIterator<Integer> iterator = list.listIterator();
        while(iterator.hasNext()) {
            System.out.print(iterator.next() + " ");
        }
        System.out.println();

        // 清空列表中的元素
        list.clear();

        // 打印清空后的列表元素
        iterator = list.listIterator();
        while(iterator.hasNext()) {
            System.out.print(iterator.next() + " ");
        }
        System.out.println();
    }
}

输出结果为：