java - 如何制作一个也考虑元素内容的优先级队列？

Question

我觉得我把事情变得过于复杂了，因为我发现有很多边界情况。这是大学的作业，所以请仅给我提示，而不是我可以复制/粘贴的代码。 我正在尝试创建一个优先级队列，对包含字符的元素进行排序。它们应根据优先级值进行排列，如果优先级存在冲突，则应按字母顺序排列。我遇到的问题是插入元素。这是我目前拥有的代码:

public void insertItem(int priority, char content) {
        boolean isSpecialCase = false;
        PList current;

        if (isEmpty()) {
            high = new PList(priority, content, null, null);
            low=high;
            System.out.println(content + " has been added to an empty list");
            isSpecialCase = true;

        }

        if (priority >= high.getPriority() && content >= high.getContent() && !isSpecialCase) {
            PList newItem = new PList(priority, content, high, null);
            high.setBehind(newItem);
            high = newItem;
            isSpecialCase = true;
            System.out.println(content + " has been added to a non empty list - highest priority");
        }
       if (priority < low.getPriority() && !isSpecialCase) {
            PList newItem = new PList(priority, content, null, low);
            low.setNext(newItem);
            low = newItem;
            isSpecialCase = true;
            System.out.println(content + " has been added to a non empty list - absolute lowest priority");
        }
        if (priority == low.getPriority() && content > low.getContent() && !isSpecialCase) {
            PList newItem = new PList(priority, content, low, low.getBehind());
            low.getBehind().setNext(newItem);
            low.setBehind(newItem);

            isSpecialCase = true;
            System.out.println(content + " has been added to a non empty list - lowest priority-highest char");

        }
        if (priority == low.getPriority() && !isSpecialCase) {
            if (content < low.getContent()) {
                PList newItem = new PList(priority, content, null, low);
                low.setNext(newItem);
                low = newItem;
                isSpecialCase = true;
                System.out.println(content + " has been added to a non empty list -lowest priority");
            }
        }



        current = high;
        while (current.getNext() != null && !isSpecialCase) {
            if (current.getPriority() >= priority) {
                if (current.getContent() > content) {
                    PList newItem = new PList(priority, content, current.getNext(), current);
                    current.getNext().setBehind(newItem);
                    current.setNext(newItem);
                    break;
                }
            }
            current = current.getNext();
        }
    }

它看起来很困惑并且有点重复，所以这就是为什么我认为我走错了路。 它适用于大多数情况，但例如当我运行时我得到一个 nullPointer:

  PriQueue p = new PriQueue();
    p.insertItem(5, 'a');
    p.insertItem(5, 'a');
    p.insertItem(4, 'x');
    p.insertItem(4, 'a');
    p.insertItem(4, 'x');

还有其他情况，它只是不将所有元素放入队列而不给出任何错误。

提前谢谢

Answer 1

我同意您使事情变得过于复杂，在没有给出完整解释的情况下，您应该考虑在您的 PList 项目上实现 Comparable 接口(interface)。然后，当您插入新项目时，您可以循环遍历列表，直到 listNode.compareTo(newNode) > 0，这就是您插入它的位置。