java - What is wrong with my Rolling Craps code? -

this question has answer here:

• what nullpointerexception, , how fix it? 12 answers

so coding game of craps requires me roll 2 dice , return sum of dice. rolling 7 or 11 wins game, rolling 2, 3, or 12 lose game. rolling 4, 5 ,6, 8, 9, 10 "establish point" user continues roll until roll same number established or until roll 7, in case lose.

in case, exception says

"exception in thread "main" java.lang.nullpointerexception @ craps.getsum(craps.java:24) @ craps.playround(craps.java:29) @ craps.main(craps.java:70) c:\users\owner\appdata\local\netbeans\cache\8.2\executor-snippets\run.xml:53: java returned: 1 build failed (total time: 2 seconds)" 

my die class looks this:

import java.util.random; public class die  {     private int number;     private random generator;      public die()     {         generator = new random();         roll();     }      public int getnumber()     {         return number;     }      public void roll()     {         number = generator.nextint(6)+1;     } } 

and game of craps looks this:

import java.util.scanner;  public class craps  {     private die die1;     private die die2;      private void rolldice()     {         die1.roll();         die2.roll();     }      private int getsum()     {         return (die1.getnumber() + die2.getnumber());     }      public void playround()     {         if (getsum() == 7 || getsum() == 11)         {             system.out.println("you rolled " +getsum()+ "! win!!!");         }         else if(getsum() == 2 || getsum() == 3 || getsum() == 12)         {             system.out.println("you rolled " +getsum()+ " lose.");         }         else if(getsum() == 4 || getsum() == 5 || getsum() == 6 || getsum() == 8 || getsum() == 9 || getsum() == 10)         {             int established = getsum();             system.out.println("establishing point... re-rolling...");             rolldice();                          {                 rolldice();                 system.out.println("you rolled " +getsum());             }             while (getsum() != established && getsum() != 7);              if (getsum() == established)             {                 system.out.println("you rolled " +getsum()+ " established point, win!");             }             else if(getsum() == 7)             {                 system.out.println("you rolled 7 after establishing point, lose.");             }          }            }      public static void main(string[] args)     {         craps game = new craps();         scanner scan = new scanner(system.in);         system.out.println("welcome game of craps!");         system.out.println("would play game? (y/n");         string input = scan.nextline();         if (input.equalsignorecase("y"))         {             game.playround();         }         else         {             system.out.println("okay see next time!");             system.exit(1);         }     } } 

private die die1; private die die2; 

holds null reference.