如何编写这个返回语句，这样我就不会返回NULL了？

Question

只是无法计算方法中的return语句。

 public LinkedList bfs_search(String numberEntered) {  
    //use a queue for all the unsearched combinations to go
    Queue<String> q = new LinkedList<String>();  

    q.add(""); 

    String possibleWord = null;

    //loop through each number entered
    for(int i = 0; i < numberEntered.length(); i++) {  
        //get the letters on the keypad for current number
        String lettersOnKeypadNumber = T9keypad[numberEntered.charAt(i) - ASCII_ZERO];  
        int len = q.size();  

        //loop while there are letter sequences in the queue.  Note len-- is same as len=len-1 so loop until only one item left in queue (the blank item inserted above)
        while(len -- > 0) {  
            String letterSequenceFromQ = q.remove();  
            //loop through each letter on the keypad number, add it to the letter sequence pulled from queue and search for that letter sequence as a word in the trie
            for(int j = 0; j < lettersOnKeypadNumber.length(); j++) {  
                possibleWord = letterSequenceFromQ + lettersOnKeypadNumber.charAt(j);  
                //q.add(tmpStr);  
                if(search(possibleWord) && possibleWord.length() == numberEntered.length()) {  
                    //found it!
                   return possibleWords(possibleWord); 

                } else {
                    //letter sequence is not a word, add it to the queue for possible word when get the next set of letters for the next keyed number
                    q.add(possibleWord);                      
                }  
            }  
        }

   } 
   return null;          
}  

Answer 1

您的方法签名是一个契约--您将返回一个链表。在这种情况下，您需要做两件事之一--返回一个链表，无论是否为空，或者如果确实存在一个包含>0项的链表，则抛出异常。

add（“”）除了允许使用len作为循环条件之外，什么也不做。使用Q.IsEmpty作为控件：您要么离开循环，要么向队列中添加字符串。

由于您正在结束if子句中的循环，请从q.add中删除else{}