Java keeps giving me an error even though there is not red line thingy -

this program made create files in specified directory user inputs. user can specify name , file extension. recent changes code marked. latest thing did code way program can tell if user added extension or of extension valid.

java.lang.exceptionininitializererror caused by: java.lang.nullpointerexception     @ filecreator.coolversion.filecreatorcoolversion.<clinit> (filecreatorcoolversion.java:13) exception in thread "main"  c:\users\deadm\appdata\local\netbeans\cache\8.2\executor- snippets\run.xml:53: java returned: 1 

^error

code:

package filecreator.coolversion;  import java.io.file; import java.io.ioexception; import java.util.*;  public class filecreatorcoolversion {  public static scanner sc = new scanner(system.in); public static boolean success = false; public static string filename; public static string filedir; public static string fileexten = filename.substring(filename.lastindexof(".") + 1); //recent change here public static file file; public static file dir;  public static void main(string[] args) throws ioexception {      system.out.println("********************************");     system.out.println("* welcome file creator 2.0! *");     system.out.println("********************************");     system.out.println(" ");      while(!success) {          system.out.println("would create file? y/n?");         string usrans = sc.nextline();          if(usrans.equalsignorecase("y")) {              system.out.println("proceeding file creation...");             break;          } else if(usrans.equalsignorecase("n")) {              system.out.println("exiting program...");             system.exit(0);          } else if(!usrans.equalsignorecase("y") || !usrans.equalsignorecase("n")) {              system.out.println("that not valid answer! please try again!");             system.out.println(" ");         }     }      while(!success) {          system.out.println(" ");         system.out.println("please enter valid filename:");         filename = sc.nextline();          if(filename.isempty()) {              system.out.println("please enter file name!");             break;          } else if(filename.contains("/") || filename.contains(":") ||                    filename.contains("*") || filename.contains("?") ||                   filename.contains("<") || filename.contains(">") ||                   filename.contains("|") || filename.contains("\"") ||                   filename.contains("\\")) {              system.out.println("please not include / \\ : * ? \" < > |");          } else if(!filename.contains(".")) {              system.out.println("please add apropriate file extensions");          } else if (!fileexten.isempty() || fileexten.contains("[^\\p{isdigit}\\p{isalphabetic}]")) { //recent change here              system.out.println("please specify valid file extension!");          } else {              system.out.println(" ");             system.out.println("file name \"" + filename + "\" chosen");             break;         }     }          system.out.println(" ");         system.out.println("where have file saved?");         system.out.println("please enter valid directory");      while(!success) {          filedir = sc.nextline();          if(!filename.contains(":")) {              system.out.println(" ");             system.out.println("please enter valid directory!");          } else if(!filename.contains("\\")) {              system.out.println(" ");             system.out.println("please enter valid directory!");          } else {              system.out.println("file directory \"" + filedir + "\" chosen");             break;         }     }      system.out.println(" ");     system.out.println("creating file...");  } 

}

i can't tell error coming please me. not @ debugging programs of , 1 of things need work on. please me.

you can't this:

public static string fileexten = filename.substring(filename.lastindexof(".") + 1); 

your file name null. inside method after filename populated.

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