1、定义链表类。 2、将链表的建立、初始化、插入、删除、输出表长、查找元素的索引位置、获取指定 位置的元素，打印整个链表等函数实现。 3、设计一个测试类，使其实际运行来测试链表类操作函数的正确性。

1. 定义链表类（LinkedList）:

public class LinkedList<T> {
    private Node<T> head; // 链表头节点
    private int length; // 链表长度

    // 构造函数
    public LinkedList() {
        head = null;
        length = 0;
    }

    // 添加新节点到链表尾部
    public void add(T data) {
        Node<T> newNode = new Node<>(data);
        if (head == null) {
            head = newNode;
        } else {
            Node<T> current = head;
            while (current.next != null) {
                current = current.next;
            }
            current.next = newNode;
        }
        length++;
    }

    // 删除指定数据的第一个出现
    public boolean remove(T data) {
        if (head == null || head.data.equals(data)) {
            if (head == head.next) {
                head = null;
            } else {
                head = head.next;
            }
            length--;
            return true;
        } else {
            Node<T> current = head;
            while (current.next != null && !current.next.data.equals(data)) {
                current = current.next;
            }
            if (current.next != null) {
                current.next = current.next.next;
                length--;
                return true;
            }
            return false;
        }
    }

    // 获取链表长度
    public int size() {
        return length;
    }

    // 查找元素的索引位置
    public int indexOf(T data) {
        Node<T> current = head;
        int index = 0;
        while (current != null) {
            if (current.data.equals(data)) {
                return index;
            }
            current = current.next;
            index++;
        }
        return -1; // 如果未找到，返回-1
    }

    // 获取指定位置的元素
    public T get(int index) {
        if (index >= 0 && index < length) {
            Node<T> current = head;
            for (int i = 0; i < index; i++) {
                current = current.next;
            }
            return current.data;
        } else {
            throw new IndexOutOfBoundsException("Index out of bounds");
        }
    }

    // 打印链表
    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        Node<T> current = head;
        while (current != null) {
            sb.append(current.data + " -> ");
            current = current.next;
        }
        sb.append("null"); // 补充末尾的空节点
        return sb.toString();
    }

    // Inner class for storing data and next reference
    private static class Node<T> {
        T data;
        Node<T> next;

        public Node(T data) {
            this.data = data;
            this.next = null;
        }
    }
}

2. 测试类（TestLinkedList）:

import org.junit.jupiter.api.Test;

public class TestLinkedList {
    @Test
    public void testLinkedListOperations() {
        LinkedList<Integer> list = new LinkedList<>();
        
        // 初始化并添加元素
        list.add(1);
        list.add(2);
        list.add(3);

        // 输出初始链表
        System.out.println("Initial list: " + list);

        // 插入、删除元素并检查
        list.add(0); // 插入
        System.out.println("After inserting 0: " + list);
        list.remove(2); // 删除
        System.out.println("After removing 2: " + list);

        // 检查大小和索引
        assert list.size() == 3;
        System.out.println("Size: " + list.size());
        assert list.indexOf(1) == 0;
        System.out.println("Index of 1: " + list.indexOf(1));

        // 获取指定位置的元素
        try {
            System.out.println("Element at index 2: " + list.get(2));
        } catch (IndexOutOfBoundsException e) {
            System.out.println(e.getMessage());
        }

        // 清空并再次打印
        list.head = null;
        System.out.println("Empty list: " + list);
    }
}