java - 我在resource.length()处得到一个空指针，但我无法弄清楚为什么？即使文件有数据

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 3 年前。

class WordCount
{
    String resource;
    void read () throws IOException
    {
         File file = new File("C:\\Users\\Desktop\\read.txt");  
         BufferedReader br = new BufferedReader(new FileReader(file)); 
         while ((resource = br.readLine()) != null)
         {
                 resource.trim();
         }
         System.out.println(resource.length());
         br.close();
    }
}

Answer 1

在这里，您在循环的最后一步分配 null:

while ((resource = br.readLine()) != null)