java - 链表的迭代器

Question

我的项目应该实现两个类。基本链表和排序链表。一切似乎都工作正常，除了由于某种原因我无法迭代排序的链表。类结构如下:

public class BasicLinkedList<T> implements Iterable<T> {
    public int size;

    private class Node {
        private T data;
        private Node next;

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

    private Node head;
    private Node tail;

    public BasicLinkedList() {
        head = tail = null;
    }
//Add, remove method 

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

            Node current = head;

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

            @Override
            public T next() {
                if(hasNext()){
                    T data = current.data;
                    current = current.next;
                    return data;
                }
                return null;
            }

            @Override
            public void remove(){
                throw new UnsupportedOperationException("Remove not implemented.");
            }

        };

现在，当我测试这个类时，它工作得很好。迭代器可以工作，我可以测试一切。问题出在扩展了这个类的排序链表类中。这是它的实现和我在构造函数中使用的比较器类:

public class SortedLinkedList<T> extends BasicLinkedList<T>{
    private class Node{
        private T data;
        private Node next;

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

    private Node head;
    private Node tail;
    private Comparator<T> comp;

    public SortedLinkedList(Comparator<T> comparator){
        super();
        this.comp = comparator;
    }

这是比较器类和我在单独的类中运行的测试:

public class intComparator implements Comparator<Integer>{
        @Override
        public int compare(Integer o1, Integer o2) {
            return o1 - o2;
        }
}

public static void main(String[] args) {
System.out.println("---------------SortedLinkedList--------------");
        SortedLinkedList<Integer> sortedList = new SortedLinkedList<Integer>(new intComparator());
        sortedList.add(3);
        sortedList.add(5);
        sortedList.add(2);
        for(int i: sortedList){
            System.out.println(i);
        }
    }   

什么也没有打印出来。我假设继承的迭代器会帮助我遍历这个，没有问题，并且显然它是合法的，因为 for-each 循环会编译。只是什么也没有打印出来。我调试了它，所有添加、删除的内容都按预期工作。只是迭代器没有做它应该做的事情。我应该为这个类创建一个单独的新迭代器吗？但这不是多余的代码吗，因为我已经继承了它？感谢帮助!

编辑:这是排序列表的添加方法

public SortedLinkedList<T> add(T element){
        Node n = new Node(element);
        Node prev = null, curr = head;
        if(head == null){
            head = n;
            tail = n;
        }
        //See if the element goes at the very front
        else if(comp.compare(n.data, curr.data) <= 0){
            n.next = head;
            head = n;
        }
        //See if the element is to be inserted at the very end
        else if(comp.compare(n.data, tail.data)>=0){
            tail.next = n;
            tail = n;
        }
        //If element is to be inserted in the middle
        else{
            while(comp.compare(n.data, curr.data) > 0){
                prev = curr;
                curr = curr.next;
            }
            prev.next = n;
            n.next = curr;
        }

        size++;
        return this;
    }

Answer 1

1) SortedLinkedList 扩展了 BasicLinkedList 但两者都有

private Node head; 
private Node tail

这是错误的。如果你想在子类中继承这些字段，你应该在父类(super class)中将这些变量标记为 protected ，然后将它们从子类中删除。

2) 私有(private)类 Node 也是如此。您在 SortedLinkedList 和 BasicLinkedList 中声明 Node 类。您应该做的是声明一次(也许在父类(super class)中？)并在两个地方使用相同的类。如果这样做，两个类都应该可以访问构造函数和字段。因此，您必须更改访问修饰符(private 是您现在拥有的)。

我将发布下面有效的代码，但我没有花任何时间进行设计。只是发布它来演示如何更改代码以使其工作。您必须决定使用哪些访问修饰符以及将类放在哪里。

import java.util.Comparator;
import java.util.Iterator;

public class Test {
    public static void main(String[] args) {
        System.out.println("---------------SortedLinkedList--------------");
        SortedLinkedList<Integer> sortedList = new SortedLinkedList<Integer>(new intComparator());
        sortedList.add(3);
        sortedList.add(5);
        sortedList.add(2);
        for (int i : sortedList) {
            System.out.println(i);
        }
    }
}

class BasicLinkedList<T> implements Iterable<T> {
    public int size;

    class Node {
        T data;
        Node next;

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

    protected Node head;
    protected Node tail;

    public BasicLinkedList() {
        head = tail = null;
    }

    // Add, remove method

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

            Node current = head;

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

            @Override
            public T next() {
                if (hasNext()) {
                    T data = current.data;
                    current = current.next;
                    return data;
                }
                return null;
            }

            @Override
            public void remove() {
                throw new UnsupportedOperationException("Remove not implemented.");
            }

        };

    }
}

class SortedLinkedList<T> extends BasicLinkedList<T> {


    private Comparator<T> comp;

    public SortedLinkedList(Comparator<T> comparator) {
        super();
        this.comp = comparator;
    }

    public SortedLinkedList<T> add(T element) {
        Node n = new Node(element);
        Node prev = null, curr = head;
        if (head == null) {
            head = n;
            tail = n;
        }
        // See if the element goes at the very front
        else if (comp.compare(n.data, curr.data) <= 0) {
            n.next = head;
            head = n;
        }
        // See if the element is to be inserted at the very end
        else if (comp.compare(n.data, tail.data) >= 0) {
            tail.next = n;
            tail = n;
        }
        // If element is to be inserted in the middle
        else {
            while (comp.compare(n.data, curr.data) > 0) {
                prev = curr;
                curr = curr.next;
            }
            prev.next = n;
            n.next = curr;
        }

        size++;
        return this;
    }
}

class intComparator implements Comparator<Integer> {
    @Override
    public int compare(Integer o1, Integer o2) {
        return o1 - o2;
    }
}