whats wrong?(NumberFormatException: null)

问题

    import java.io.*;
    class AccountInfo {

    private String lastName;
    private String firstName;
    private int age;
    private float accountBalance;
    protected AccountInfo(final String last,final String first,final int ag,final float balance) throws IOException{

        lastName=last;
        firstName=first;
        age=ag;
        accountBalance=balance;
    }
    public void saveState(final OutputStream stream){try{

        OutputStreamWriter osw=new OutputStreamWriter(stream);
        BufferedWriter bw=new BufferedWriter(osw);
        bw.write(lastName);
        bw.newLine();
        bw.write(firstName);
        bw.write(age);
        bw.write(Float.toString(accountBalance));
        bw.close();}
        catch(IOException e){
            System.out.println (e);
        }
    } 
    public void restoreState(final InputStream stream)throws IOException{
        try{


            InputStreamReader isr=new InputStreamReader(stream);
            BufferedReader br=new BufferedReader(isr);
            lastName=br.readLine();
            firstName=br.readLine();
            age=Integer.parseInt(br.readLine());
            accountBalance=Float.parseFloat(br.readLine());
            br.close();}
            catch(IOException e){
                System.out.println (e);
        }

    }

}
    class accounto{
        public static void main (String[] args) {try{



            AccountInfo obj=new AccountInfo("chaturvedi","aayush",18,18);
            FileInputStream fis=new FileInputStream("Account.txt");
            FileOutputStream fos=new FileOutputStream("Account,txt");
            obj.saveState(fos);
            obj.restoreState(fis);}
            catch(IOException e){
                System.out.println (e);
        }
    }
}

im getting the following error: Exception in thread "main" java.lang.NumberFormatException: null at java.lang.Integer.parseInt(Integer.java:454) at java.lang.Integer.parseInt(Integer.java:527) at AccountInfo.restoreState(accounto.java:43) at accounto.main(accounto.java:60)

回答1:

This is your code:

BufferedReader br=new BufferedReader(isr);
//...
age=Integer.parseInt(br.readLine());

And here is the documentation of BufferedReader.readLine() (bold mine):

A String containing the contents of the line, not including any line-termination characters, or null if the end of the stream has been reached

In fact, you never really check whether EOF was reached. Can you be that certain about your input (turns out you can't).

Also for Integer.parseInt():

Throws:

NumberFormatException - if the string does not contain a parsable integer.

null is hardly a "parsable integer". The simplest solution is to check your input and handle errors somehow:

String ageStr = br.readLine();
if(ageStr != null) {
  age = Integer.parseInt(br.readLine())
} else {
  //decide what to do when end of file
}

回答2:

From this line:

Integer.parseInt(br.readLine());

So it looks like you're reading the end of the stream so br.readLine() is null. And you can't parse null into an int.

回答3:

The br.readLine() method is returning null, which can't be converted into an Integer - the likely reason for this is that the end of the stream has been reached.

回答4:

1. I think the value returned from br.readLine() is null.

2. So it can NOT be converted from String to Integer.

3. Thats the reason you are getting NumberFormatException

4. To handle this, Wrap that code into try/catch block.

 try{

        age = Integer.parseInt(br.readLine());


  }catch(NumberFormatException ex){


        System.out.println("Error occured with during conversion");
 }

来源：https://stackoverflow.com/questions/11600699/whats-wrongnumberformatexception-null

标签

java

numberformatexception