where iam going wrong?? no matter says null pointer exception on string.replace() want replace charecter file , write changed content other file.. though easy unable write it.help please!
package tinku; /* * change license header, choose license headers in project properties. * change template file, choose tools | templates * , open template in editor. */ import java.io.bufferedreader; import java.io.bufferedwriter; import java.io.dataoutputstream; import java.io.file; import java.io.filenotfoundexception; import java.io.fileoutputstream; import java.io.filereader; import java.io.filewriter; import java.io.ioexception; import java.io.inputstreamreader; import java.io.linenumberreader; import java.util.scanner; /** * * @author gajasurve */ public class tinku { static int i; /** * @param args command line arguments */ public static void main(string[] args) throws filenotfoundexception, ioexception { // todo code application logic here string str; final string y; string key; fileoutputstream fos = new fileoutputstream("/home/gajasurve/desktop/done2.txt"); dataoutputstream output = new dataoutputstream(fos); bufferedreader r = new bufferedreader(new inputstreamreader(system.in)); system.out.println("\n enter complete file path extension (ex: /home/gajasurve/desktop/info.txt) : "); string source; source=r.readline(); system.out.print("enter key element find in file "); key=r.readline(); file f= new file(source); linenumberreader lr= new linenumberreader(new filereader(f)); while((str=lr.readline())!=null) { if(str.contains(key)) { i=lr.getlinenumber(); system.out.print("the entered key element can b found in " + + " line"); } } system.out.println("do u wish change key element? y|n"); string dec= r.readline(); switch (dec) { case "y" : system.out.print("enter new key element replace"); string d2; d2 = r.readline(); str= str.replaceall(key, d2); //npe here system.out.println(str); break; } } }
when run while loop, exit condition loop ends when str becomes null, hence when trying access str next time null , gives nullpointerexception.
you can fix running similar while loop around replaceall() code, or can move until replaceall() method call inside while loop. (note: ask if want replace key every occurrence)
possible fixed code:
package tinku; /* * change license header, choose license headers in project properties. * change template file, choose tools | templates * , open template in editor. */ import java.io.*; /** * * @author gajasurve */ public class tinku { static int i; /** * @param args command line arguments */ public static void main(string[] args) throws filenotfoundexception, ioexception { // todo code application logic here string str; final string y; string key; bufferedreader br = new bufferedreader(new inputstreamreader(system.in)); system.out.println("\n enter complete file path extension (ex: /home/gajasurve/desktop/info.txt) : "); string source; source = br.readline(); file f= new file(source); linenumberreader lr= new linenumberreader(new filereader(f)); system.out.print("enter key element find in file : "); key = br.readline(); while((str = lr.readline()) != null) { if(str.contains(key)) { = lr.getlinenumber(); system.out.println("the entered key element can b found in " + + " line"); } } lr.close(); system.out.println("do u wish change key element? y|n"); string dec= br.readline(); switch(dec) { case "y" : { system.out.print("enter string replace key : "); string d2; d2 = br.readline(); lr= new linenumberreader(new filereader(f)); string outputfile = "/home/gajasurve/desktop/done2.txt"; printwriter pw = new printwriter(new filewriter(outputfile)); while((str = lr.readline()) != null) { if(str.contains(key)) { pw.println(str.replaceall(key, d2)); } else { pw.println(str); } } pw.close(); break; } } } } 
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