空指针异常与objectinputstream

Question

我想读这个名单和电话号码列表中，但该程序不断抛出nullpointerexception。它为什么这样做？

int i=0; 
     Datab[] b = null; 
     //b = null; 

     // The name of the file to open. 
     String fileName = "datt.dat"; 

     try { 
      // Use this for reading the data. 
      byte[] buffer = new byte[1000]; 
      FileInputStream FileIS = new FileInputStream("datt.dat"); 
      ObjectInputStream input = new ObjectInputStream(FileIS); 

      for(i=0; i<b.length; i++) 
      b[i]=(Datab)input.readObject(); 

      input.close(); 

Answer 1

b为null，那么将b.length抛出