java - 如何将 addElement 方法写入已排序的 LinkedList？

Question

我有一个作业:

implement a linked list of String objects by use of the class Node (see Big >Java Early Objects 16.1.1). Write methods, that make it possible to insert >and delete objects, as well as print all objects in the list. It is a >requirement that all elements in the list are sorted, at all times, according >to the natural ordering of Strings(Comparable).

我似乎无法正确使用的方法是 addElement 方法

全类同学都在这里:https://pastebin.com/Swwn8ykZ主应用程序:https://pastebin.com/A22MFDQk

我读过这本书(Big Java Early Objects)，也看过 geeksforgeeks

public void addElement(String e) {
    Node newNode = new Node();
    if (first.data == null) {
        first.data = e;
        System.out.println("Success! " + e + " has been 
added!");
    } else if (first.data.compareTo(e) == 0) {
        System.out.println("The element already exists in the 
list");
    } else {
        while (first.next != null) {
            if (first.next.data.compareTo(e) != 0) {
                first.next.data = e;
            } else {
                first.next = first.next.next;
            }
        }
    }
}

public static void main(String[] args) {
    SortedLinkedList list = new SortedLinkedList();

    String e1 = new String("albert");
    String e2 = new String("david");
    String e3 = new String("george");
    String e4 = new String("jannick");
    String e5 = new String("michael");

    // ----------------SINGLE LIST--------------------------
    list.addElement(e1);
    list.addElement(e2);
    list.addElement(e3);
    list.addElement(e4);
    list.addElement(e5);

    System.out.println("Should print elements after this:");
    list.udskrivElements();
 }
}

预期结果:五个名字打印在列表中

实际结果:打印的名字

Answer 1

给定这个 Node 类:

private class Node {
    public String data;
    public Node next;
}

和一个 private Node first; 的类级字段，最初为 null 表示一个空列表，addElement 可能是这样的:

public void addElement(String text) {
    if (text == null) return; // don't store null values

    Node extra = new Node();
    extra.data = text;

    if (first == null) {
        // no list yet, so create first element
        first = extra;
    } else {
        Node prev = null; // the "previous" node
        Node curr = first; // the "current" node

        while (curr != null && curr.data.compareTo(text) < 0) {
            prev = curr;
            curr = curr.next;
        }

        if (curr == null) {
            // went past end of list, so append
            prev.next = extra;
        } else if (curr.data.compareTo(text) == 0) {
            System.out.println("Already have a " + text);
        } else {
            // between prev and curr, or before the start
            extra.next = curr;
            if (prev != null) {
                prev.next = extra;
            } else {
                // append before start, so 'first' changes
                first = extra;
            }
        }
    }
}

顺便说一下，还可以尝试以未排序的顺序添加名称，以检查列表是否对它们进行排序(当我尝试这样做时，我在代码中发现了一个错误)。