Something wrong with random generator...

Question

Hi guys, im having a problem with my code. For some reason my code is not generating a number for me. Instead of pasting ALL of the code related to it, ill just state my variables and give the code thats related.
import java.util.*;
public static Random randomGenerator;
randomGenerator = new Random();
ok this is the code(ignore the system.out.println, i was using it to check where the problem in my code was):
public static void stochasticHillClimberSearch(int lecture, int studentID){
//methods ommited//
for(int i = 0; i < anyAscent; i++){
int chooseRoom = 0;
int chooseTeacher = 0;
fitnessValue = 0;
System.out.println("Made into loop");
//randomly choose the solutions for our search
int chooseDay = randomGenerator.nextInt(5);
int chooseTime = 1;
System.out.println("made through genetaor"+chooseDay);
calculateRoomFitness(chooseDay,chooseTime,chooseRoom,studentID); //call the room fitness method using variables declared
calculateTeacherFitness(chooseDay,chooseTime,chooseTeacher,module); //call the teacher fitness method using variables declared
calculateStudentFitness(chooseDay,chooseTime,studentID); //call the student fitness method using variables declared
compareFitnessValues(fitnessValue,chooseDay,chooseTime,chooseTeacher,chooseRoom); //compare the fitness value method
The problem is my number is not generating, my terminal is printing:
Made into loop
made through genetaor
Made into loop
made through genetaor
Made into loop
made through genetaor
Made into loop
and you'll notice that there is no number printed. The error im getting is:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
     at ConstraintSearch.doRandom(ConstraintSearch.java:175)
     at ConstraintSearch.stochasticHillClimb(ConstraintSearch.java:147)
     at Main.anyAscentSearch(Main.java:303)
     at Main.stochButtonPress(Main.java:1111)
     at Main.access$1500(Main.java:16)
I don't have any idea where the nullpointer is coming from, but im hoping one of you guys are able to tell me :). Many thanks in advance

Answer 1

jennylijava wrote:
How is the randomGenerator null? Since you've shown neither your real code, nor an SSCCE, with code tags and indentation, of course, I can't answer that.
However, if that's line 175, then it absolutely IS null.
Ive initialised the randomGenerator by typing:
randomGenerator = new Random() in my constructor method.So you claim. The JVM thinks otherwise. I'm more inclined to believe it than you (or any other programmer, including myself).
My guess, based on the limited information you've provided, is that either a) you're never calling that constructor, or b) that constructor has a local variable that's hiding the member variable.
Edited by: jverd on Feb 22, 2009 2:02 PM