java - Java中向单链表添加元素

Question

我正在用 Java 实现一个单链表。我不喜欢这段代码的是每次添加元素时都需要检查 if (head.next == null) 。但该条件仅在添加第一个元素时满足一次。

有没有办法在没有这样的条件的情况下实现单链非循环列表？

package sample;

import java.util.Iterator;
import java.util.NoSuchElementException;

public class SinglyLinkedList<T> implements Iterable<T> {

    private Node<T> head = new Node<T>(null);
    private Node<T> last = null;

    public SinglyLinkedList(T... elements) {
        addAll(elements);
    }

    public void add(T element) {
        if (head.next == null) {
            head.next = new Node<T>(element);
            last = head.next;
        } else {
            Node<T> newNode = new Node<T>(element);
            last.next = newNode;
            last = last.next;
        }
    }

    public void addAll(T... elements) {
        for (T element : elements) {
            add(element);
        }
    }

    @Override
    public String toString() {
        Iterator<T> iterator = iterator();
        if (!iterator.hasNext()) {
            return "[]";
        }
        StringBuilder builder = new StringBuilder();
        builder.append("[");
        while (iterator.hasNext()) {
            T element = iterator.next();
            builder.append(element);
            if (!iterator.hasNext()) {
                return builder.append("]").toString();
            }
            builder.append(", ");
        }
        return builder.toString();
    }

    @Override
    public Iterator<T> iterator() {
        return new Iterator<T>() {

            Node<T> current = head;

            @Override
            public boolean hasNext() {
                return current.next != null;
            }

            @Override
            public T next() {
                if (!hasNext()) {
                    throw new NoSuchElementException();
                }
                Node<T> temp = current;
                current = current.next;
                return temp.next.element;
            }

        };
    }

    private static class Node<T> {

        private Node<T> next;
        private T element;

        Node(T element) {
            this.element = element;
        }

        @Override
        public String toString() {
            return element.toString();
        }
    }
}

Answer 1

您可以将 last 初始化为指向 head，然后您的 if 是多余的:

private Node<T> head = new Node<T>(null);
private Node<T> last = head;

public void add(T element) {
        Node<T> newNode = new Node<T>(element);
        last.next = newNode;
        last = last.next;
}