Java - Reading input from a file. java.io.FilterInputStream.available(Unknown Source)? -

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i haven't written java in years , went refresh memory simple 'read-from-file' example. here code..

import java.io.*; public class filereading {      public static void main(string[] args) {         file file = new file("c:\\file.txt");         fileinputstream fs = null;         bufferedinputstream bs = null;         datainputstream ds = null;          try         {             fs = new fileinputstream(file);             bs = new bufferedinputstream(bs);             ds = new datainputstream(ds);              while(ds.available()!= 0)             {                 string readline = ds.readline();                 system.out.println(readline);             }              ds.close();             bs.close();             fs.close();         }          catch(filenotfoundexception e)         {             e.printstacktrace();         }         catch(ioexception e)         {             e.printstacktrace();         }     } }

this compiles fine (although apparently ds.readline() deprected), @ runtime, gives me

exception in thread "main" java.lang.nullpointerexception @ java.io.filterinputstream.available(unknown source) @ filereading.main(filereading.java:21)

what gives?

you made simple typo:

ds = new datainputstream(ds);

should be

ds = new datainputstream(bs);

your code initializing datainputstream null source, since ds hasn't been created yet.

having said that, jon skeet's answer gives better way write file-reading program (and should use readers/writers rather streams when dealing text).


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