Java.NullPointerException null (again)

问题:

I am having another problem with NullPointerException. This time it is highlighting tellen = telno.length(). Beore you ask:

• There is data in the text file to be read to that variable.
• All variables were initialized.
• Buffered Reader is also initialized.

• Here is a snippet of my code:

  while((telno = br.readLine()) != null){
      name = br.readLine();
  
      surname = br.readLine();
  
      company = br.readLine();
  
      house = br.readLine();
  
      street = br.readLine();
  
      locality = br.readLine();
  
      postcode = br.readLine();
  
      telno = br.readLine();
      tellen = telno.length();
  
      mobno = br.readLine();
  
      sep = br.readLine();
  
      if(tellenx > tellen) tellen = tellenx;
  
  
  }
  

Please help. Thanks. Text file:

• Name
• Surname
• Company
• House
• Street
• Locality
• Telephone number
• Mobile Number

Problem is in the telephone (tellen) All these names are fictional, and this program is a telephone directory

George
Farrugia
Some Company 
9, Flowers
Quail Street
Bubaqra
BBQ 1569
21369854
79825643
--------------------------------------------
Paul
Zammit

9
Bird Street
St. Julians
STJ 0000
21545796
79745247
--------------------------------------------
Peter
Spiteri
Oak Company
Trees
Birch Street
Oakgrove
TRE 3333
21323323
99323323
--------------------------------------------

The blank after Zammit is a space. That is placed if there is no data to avoid a problem like this.

回答1:

This error is getting caused because you are reading 11 lines in one while loop instead you have to read 10 lines only.

So at some point br.readLine() will return null.

You need to read file according to your need that means in one go (your while loop) read 10 lines, then next 10 lines and so on.

while((telno = br.readLine()) != null){ // first line
    name = br.readLine();   // secondline I think this should be first line

    surname = br.readLine();

    company = br.readLine();

    house = br.readLine();

    street = br.readLine();

    locality = br.readLine();

    postcode = br.readLine();

    telno = br.readLine();
    tellen = telno.length();

    mobno = br.readLine();

    sep = br.readLine();  // eleventh line

    if(tellenx > tellen) tellen = tellenx;


}

回答2:

Most probably its the end of the file and your bufferedReader.readLine() is returning null and you just invoked a method on an instance which is null, which leads to NPE.

回答3:

I guess you are trying to read using readLine() without null check.Definitel, it will give NPE.

回答4:

Adding an if statement to check if there is any null references is a good practice to check for an error in your code.

An example in pseudo code would be:

   telno = br.readLine();

   if(telno == null)
       System.out.println("this will cause null pointer exception  "+ telno.length()); 
   else
       tellen = telno.length();