java - 双向链接Lisl不断出现空指针错误

我看了所有前面的例子，看不到我做错了什么。由于某种原因，我真的在与空指针异常作斗争，而我只是无法将它们包裹住。

public class DLBDictionary implements DictionaryInterface {
//Store Strings in an Node

public DLBNode firstNode;

public class DLBNode
{

    public char value;
    public DLBNode nextValue;
    public DLBNode nextLetter;

    public DLBNode(){
        this.value = '/';
        this.nextValue = null;
        this.nextLetter = null;
    }

    public DLBNode(char value){
        this.value = value;
        this.nextValue = null;
        this.nextLetter = null;
    }
}

public DLBDictionary() {
    DLBNode firstNode = new DLBNode('/');
}

// Add new String to end of list.  If String should come before
// previous last string (i.e. it is out of order) sort the list.
// We are keeping the data sorted in this implementation of
// DictionaryInterface to make searches a bit faster.
public boolean add(String s) {
    int charIndex = 0;
    while(charIndex<=s.length())
    {
        char currentChar = s.charAt(charIndex);
        boolean added = false;
        while(!added)
        {
            if(firstNode.value == '/')
            {
                firstNode.value = currentChar;
                added = true;
            }
            else if(firstNode.value == currentChar)
            {
                if(firstNode.nextLetter == null)
                {
                    DLBNode newNode = new DLBNode();
                    firstNode.nextLetter = newNode;
                    firstNode = firstNode.nextLetter;
                }
                else
                {
                    firstNode = firstNode.nextLetter;
                }
                added = true;
            }
            else
            {
                firstNode = firstNode.nextValue;
            }
        }
        charIndex++;
    }
    DLBNode tempNode = new DLBNode('^');
    firstNode.nextLetter = tempNode;
    return true;
}

我省略了其余的代码，但最后一个if语句是我得到异常的地方。对我来说完全是无稽之谈！我不是在构造函数中将firstNode的值初始化为'/'吗？因此，firstNode.getValue应该返回'/'而不是空指针异常。

最佳答案

你应该做
this.firstNode = new DLBNode（）;
在DLBDictionary的构造函数中。您实际上是在创建一个新对象，而不是初始化firstNode。希望能帮助到你。