单链表的添加和删除元素

public class LinkedList<E> {
  private Node head;
  private int size;

  public LinkedList() {
      this.head = null;
      this.size = 0;
  }

public void add(int index, E e) {
    if (index < 0 || index > size) {
        throw new IllegalArgumentException("index 错误");
    }

    if (index == 0) {
        addFirst(e);
    } else {
        Node prev = head;
        for (int i = 0; i < index - 1; i++) {
            prev = prev.next;
        }
        Node node = new Node(e);
        node.next = prev.next;
        prev.next = node;
        size++;
    }

}

public void addFirst(E e) {
    Node node = new Node(e);
    node.next = head;
    head = node;
    size++;
}

public int getSize() {
    return size;
}

public boolean isEmpty() {
    return size == 0;
}

public E remove(int index) {
    if (index < 0 || index > size) {
        throw new IllegalArgumentException("索引错误");
    }
    if (index == 0) {
        return removeFirst();
    } else {
        Node prev = head;
        for (int i = 0; i < index - 1; i++) {
            prev = prev.next;
        }
        Node removeNode = prev.next;
        prev.next = removeNode.next;
        removeNode.next = null;
        size--;
        return removeNode.e;
    }

}

public E removeFirst() {
    Node node = head;
    head = head.next;
    size--;
    return node.e;
}

@Override
public String toString() {
    StringBuilder str = new StringBuilder();
    Node node = this.head;
    while (node != null) {
        str.append(node.e);
        str.append("->");
        node = node.next;
    }
    str.append("NULL");
    return str.toString();
}

private class Node {
    public Node next;
    public E e;

    public Node(Node next, E e) {
        this.next = next;
        this.e = e;
    }

    public Node() {
        this(null, null);
    }

    public Node(E e) {
        this(null, e);
    }
}
}