Please help with search function

Question

Heya, im currently working on code that will allow me to add, view, search and remove prisoners and wardens from a prison system. So far i have managed to allow the user to add and view. Im a bit stuck on the search part of the code, its a bit temperamental :S, sometimes it will find and display the data, but other times it will not and comes up with the error
Exception in thread "main" java.lang.NullPointerException
at Prison.getNum(Prison.java:128)
at TestPrison.main(TestPrison.java:101)
Below i have put my Prison and TestPrison Class files and highlighted the lines the compiler said had the error, any help would be really appreciated because i really cant work out wats going on.
Prison
public class Prison
private Prisoner [] thePrisoner;
private Warden [] theWarden;
private HighPrisoner [] theHighPrisoner;
private int maxP;
private int maxPrisoners;
private int maxW;
private int maxWardens;
private int maxH;
private int maxHighPrisoners;
public String prisonName;
public Prison (String prison, int maxP, int maxW, int maxH)
prisonName = prison;
maxPrisoners = maxP;
maxP = 0;
thePrisoner = new Prisoner [maxPrisoners];
maxWardens = maxW;
maxW = 0;
theWarden = new Warden [maxWardens];
maxHighPrisoners = maxH;
maxH = 0;
theHighPrisoner = new HighPrisoner [maxHighPrisoners];
public boolean addPrisoner( Prisoner newPrisoner )
if ( maxP == maxPrisoners )
System.out.println("Prisons full");
return false;
else
System.out.println("Prisoner now in Prison");
thePrisoner[maxP] = newPrisoner;
maxP++;
return true;
public boolean addHighPrisoner( HighPrisoner newHighPrisoner )
if ( maxH == maxHighPrisoners )
System.out.println("Prisons full");
return false;
else
System.out.println("High Level Prisoner now in Prison");
theHighPrisoner[maxH] = newHighPrisoner;
maxH++;
return true;
public boolean addWarden( Warden newWarden )
if ( maxW == maxWardens )
System.out.println("We Have Anough Wardens");
return false;
else
System.out.println("Warden now working at Prison");
theWarden[maxW] = newWarden;
maxW++;
return true;
public void outputAll()
System.out.println("School Name: " + prisonName );
     System.out.println("");
outputWardens();
     System.out.println("");
     outputPrisoners();
     System.out.println("");
outputHighPrisoners();
System.out.println("");
public void outputWardens()
System.out.println("The Wardens:");
for( int i=0; i < maxW; ++i)
System.out.println(theWarden);
public void outputPrisoners()
System.out.println("The Low Level Prisoners:");
for( int i=0; i < maxP; ++i)
System.out.println(thePrisoner[i]);
public void outputHighPrisoners()
System.out.println("The High Level Prisoners:");
for( int i=0; i < maxH; ++i)
System.out.println(theHighPrisoner[i]);
public void getNum(String num)
System.out.println("---------------");
System.out.println("Search for Prisoner ID:");
System.out.println("---------------");
for(Prisoner nextPrisoner : thePrisoner)
     --> 128     if (nextPrisoner.getNum() == num)
          System.out.println(nextPrisoner);
else
System.out.println("Sorry no Prisoner ID found");
for(HighPrisoner nextHighPrisoner : theHighPrisoner)
          if (nextHighPrisoner.getNum() == num)
          System.out.println(nextHighPrisoner);
else
System.out.println("Sorry No Prisoner ID found");
System.out.println("");
TestPrison
import java.util.*;
public class TestPrison
public static void main(String []args)
     String sN;
int sS;
     String sA;
     String tN;
int tS;
     int input;
String aN;
int aS;
String aA;
int aL;
String aC;
String pN;
String rN;
     Scanner kybd = new Scanner(System.in);
     Prison prison0 = new Prison("Alcatraz",200,200,100);
     do {
          menu();
          System.out.println("Enter Option: ");
          input = kybd.nextInt();
          switch(input) {
          case 1:
               System.out.println("Enter Name: ");
               tN = kybd.next();
               System.out.println("Enter Rank: ");
               tS = kybd.nextInt();
               Warden wardenObject = new Warden(tN,tS);
               prison0.addWarden(wardenObject);
               System.out.println("\nWarden "+tN+" Added!");
               break;
case 2:
System.out.println("Enter Prisoner Security Level: ");
aL = kybd.nextInt();
if (aL > 3)
System.out.println("Enter Name: ");
               aN = kybd.next();
               System.out.println("Enter Remaining Jail Time: ");
               aS = kybd.nextInt();
               System.out.println("Enter Prisoner ID: ");
               aA = kybd.next();
System.out.println("Can Prisoner Share Cell? ");
aC = kybd.next();
               HighPrisoner highprisonerObject = new HighPrisoner(aN,aS,aA,aL,aC);
               prison0.addHighPrisoner(highprisonerObject);
               System.out.println("\nPrisoner " + aA + " Added!");
               break;
else
System.out.println("Enter Name: ");
               sN = kybd.next();
               System.out.println("Enter Remaining Jail Time: ");
               sS = kybd.nextInt();
               System.out.println("Enter Prisoner ID: ");
               sA = kybd.next();
               Prisoner prisonerObject = new Prisoner(sN,sS,sA);
               prison0.addPrisoner(prisonerObject);
               System.out.println("\nPrisoner " + sA + " Added!");
               break;
          case 3:
               prison0.outputAll();
               break;
          case 4:
               prison0.outputWardens();
               break;
          case 5:
               prison0.outputPrisoners();
     break;
case 6:
prison0.outputHighPrisoners();
break;
case 7:
prison0.outputPrisoners();
prison0.outputHighPrisoners();
break;
case 8:
System.out.println("Enter Prisoner ID: ");
               pN = kybd.next();
---> 101 prison0.getNum(pN);
break;
          default:
               System.out.println("Error Selection Does Not Exist");
               break;
     } while(input >= 0);
public static void menu() {
     System.out.println("");
     System.out.println("MAIN MENU");
     System.out.println("*********\n");
     System.out.println("1. Add Warden\n");
System.out.println("2. Add Prisoner\n");
     System.out.println("3. View All\n");
     System.out.println("4. View Wardens\n");
     System.out.println("5. View Low Level Prisoners\n");
System.out.println("6. View High Level Prisoners\n");
System.out.println("7. View All Prisoners\n");
System.out.println("8. Search Prisoner ID\n\n");
Once again any help would really be appreciated : )

Answer 1

The nextPrisoner is null, and you can't call getNum() on a null reference.
Try replacing that line with:if (nextPrisoner != null && nextPrisoner.getNum() == num) Oh, next time you're posting code, please use code tags:
http://forum.java.sun.com/help.jspa?sec=formatting