添加和删​​除链接列表

Question

我正在处理一个在链接列表中添加和删除内容的类。我现在已经调试了大约一个小时，一切看起来都运行良好，但仍然没有得到正确的输出。我的方法是：

/ IMPLEMENT -- adds a book to the end of the linked list
public void add(Book b) {
    BookNode curr = head;
    // BookNode curr = head;
    if (head == null) {
        BookNode book = new BookNode(b);
        head = book;
        size++;

    } else {
        for (; curr.getNext() != null; curr = curr) {
            curr = curr.getNext();

        }
        BookNode book1 = new BookNode(b);
        curr.setNext(book1);
        size++;
    }
}

// IMPLEMENT -- adds a book at the specific index, or at the end if index is
// greater than size
public void add(Book b, int index) {
    BookNode curr = head;
    if(head == null){
        BookNode book = new BookNode(b);
        head = book;
        size++;
    }

    if (index > size) {
        for (; curr.getNext() != null; curr = curr) {
            curr = curr.getNext();

        }
        BookNode book1 = new BookNode(b);
        curr.setNext(book1);
        size++;
    }
    if (index == 0) {
        head = new BookNode(b, head);
    } else {
        for (int i = 0; i < index - 1; i++) {
            curr = curr.getNext();
        }
        curr.setNext(new BookNode(b, curr.getNext()));
    }
    size++;
}

// IMPLEMENT -- removes a book and returns it, or returns null if it is not
// present
public Book remove(Book b) {
    if (head == null) {
        return null;
    }
    if (head.getBook().equals(b)) {
        BookNode r = head;
        head = head.getNext();
        size--;
        return r.getBook();
    } else {
        BookNode curr = head;
        for (; curr.getNext() != null; curr = curr.getNext()) {
            // curr = curr.getNext();
            if (curr.getNext().getBook().equals(b)) {
                BookNode a;
                a = curr.getNext();
                curr.setNext(curr.getNext().getNext());
                size--;
                return a.getBook();
            }
        }

    }
    return null;
}

// IMPLEMENT -- removes a book at a specific indexand returns it,
// or returns null if it is not present
public Book remove(int index) {
    BookNode b;
    if (index < 0 || index >= size) {
        return null;
    }
    if (index == 0) {
        // head = head.getNext(); // first return
        b = head;
        head = head.getNext();
        size--;
        return b.getBook();

    } else {
        BookNode curr = head;
        for (int i = 0; i < index; i++) {
            curr = curr.getNext(); // removes from list index
        }
        b = curr;
        curr.setNext(curr.getNext().getNext());
        size--;
        return b.getBook();
    }
}

所以所有的方法都在运行和工作，但是一旦它删除了一本书然后查找它就不会像它应该的那样返回null。而且在将列表添加到列表末尾时也遇到了问题。我把它缩小了，看起来我的删除方法（索引）出了问题。