Question

我查看了之前的所有示例，无法看到任何我做错的事情。由于某种原因，我真的很挣空指针异常，我只是无法绕过它们。

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;
}

我离开了我的其余代码，但最后的if语句是我得到异常的地方。对我来说完全是无稽之谈！我没有将firstNode的值初始化为＆＃39; /＆＃39;在构造函数中？所以firstNode.getValue应该返回＆＃39; /＆＃39;不是空指针异常。

Answer 1

你应该这样做 this.firstNode = new DLBNode（）; 在DLBDictionary的构造函数中。您实际上正在创建一个新对象，而不是初始化您的firstNode。希望它有所帮助。

Answer 2

You reset firstNode with several statements in the loop:

 firstNode = firstNode.nextValue;

因此会发生firstNode == null，这会导致NPE。 char值与它无关，它将被初始化为值为0x00的字符。

双链接Lisl不断获取空指针错误

2 个答案: