java - Nullpointer Exception reading in file line by line -

txt file reading program line line. goal display text no punctuations , in lowercase. far able display text in way code below keep receiving run-time error of nullpointer exception @ last line of "while" expression , not sure error is. believe problem may have been in boolean while expression , tried changing input != null reader.readline() != null no success. thank you!

import java.io.filereader; import java.io.bufferedreader; import java.io.filenotfoundexception; import java.io.ioexception;  public class binarytree {      public static void main(string[] args) {          string inputfile = "pg345.txt";         filereader filereader = null;          try {             filereader = new filereader(inputfile);         }   catch (filenotfoundexception e) {                 e.printstacktrace();         }          bufferedreader reader = new bufferedreader(filereader);         string input;          try {             input = reader.readline().tolowercase().replaceall("[^a-za-z ]", "").tolowercase();             system.out.println(input);             while (input != null) {                   input = reader.readline().tolowercase().replaceall("[^a-za-z ]", "").tolowercase();                 system.out.println(input);             }           } catch (ioexception e) {             // todo auto-generated catch block             e.printstacktrace();         }          try {             filereader.close();         }   catch (ioexception e) {             e.printstacktrace();         }          }   } 

your culprit is

reader.readline().tolowercase().replaceall("[^a-za-z ]", "").tolowercase() reader.readline().tolowercase().replaceall("[^a-za-z ]", "").tolowercase(); 

here invocation

reader.readline() 

might return null if there no more lines in file.