Exception Error

[Sotsiak]

Hello hello, I write a java program for my university, right know I havent completed it yet but it runs ok.
First of all here is the code :

import java.io.*;
import java.util.Calendar;
import java.text.SimpleDateFormat;

class UserInput {
 public static String getString() {
  String line;
  InputStreamReader input=new InputStreamReader(System.in);
  BufferedReader in=new BufferedReader(input);
  try {
   line=in.readLine();
   return line;
  }
  catch(Exception e) {
  return "Exception";
  }
 }

 public static int getInteger() {
  String line;
   InputStreamReader input=new InputStreamReader(System.in);
   BufferedReader in=new BufferedReader(input);
 try {
  line=in.readLine();
  int i=Integer.parseInt(line);
  return i;
 }
 catch(Exception e) {
 return -1;
  }
 }
}

class Vehicle{
    private int number;
    private String sign;
    private String type;
    private String time;
    private int position;

    public Vehicle(int number, String sign, String type, String time, int position){
        this.number=number;
        this.sign=sign;
        this.type=type;
        this.time=time;
        this.position=position;
    }

    public Vehicle(){
        number=-1;
        sign=" ";
        type=" ";
        time=" ";
        position=-1;
    }

    public void setNumber(int n){
        number=n;
    }

    public void setSign(String s){
        sign=s;
    }

    public void setType(String t){
        type=t;
    }

    public void setTime(String t){
        time=t;
    }

    public void setPosition(int p){
        position=p;
    }

    public int getNumber(){
        return number;
    }

    public String getSign(){
        return sign;
    }

    public String getType(){
        return type;
    }

    public String getTime(){
        return time;
    }

    public int getPosition(){
        return position;
    }
}

class MyUtils{
    public static final String DATE_FORMAT_NOW = "HH:mm:ss";
    public static String findTime(){
        Calendar cal = Calendar.getInstance();
        SimpleDateFormat sdf = new SimpleDateFormat(DATE_FORMAT_NOW);
        return sdf.format(cal.getTime());
    }

    public static int seq_search(Vehicle table[], String findSign){
        for(int i=0; i<table.length; i++){
            if(table[i].getSign().equals(findSign))
                return i;
        }
        return -1;
    }

    public static int bin_search(Vehicle table[], int findPosition){
        int left=0;
        int right=table.length-1;
        int mid;
        int pos=-1;

        while(pos==-1&&left<=right){
            mid=(left+right)/2;
            [B]if(findPosition<table[mid].getPosition())[/B]
                right=mid-1;
            else if(findPosition>table[mid].getPosition())
                left=mid+1;
            else pos=mid;
        }
        return pos;
    }

    public static int protropi(boolean table[]){
        for(int i=0; i<table.length; i++){
            if(table[i]==false)
                return i;
        }
        return -1;
    }

    public static void printVehicle(int i, Vehicle table[]){
        System.out.println("Aukson Arithmos: "+table[i].getNumber());
        System.out.println("Pinakida: "+table[i].getSign());
        System.out.println("Typos: "+table[i].getType());
        System.out.println("Hmeromhnia: "+table[i].getTime());
        System.out.println("Thesi: "+table[i].getPosition()+1);
    }
}

public class VehicleDemo{
    public static void main(String args[]) throws IOException{

        int choice;
        int counter=1;
        int number;
        String sign;
        String type;
        String time;
        int position;

        Vehicle table[]=new Vehicle[10];
        boolean theseis[]=new boolean[10];
        
        for(int i=0; i<theseis.length; i++)
            theseis[i]=false;

        boolean menu=false;
        do{

        System.out.println("      Arxiko menu");
        System.out.println("1. Proselefsi Oximatos");
        System.out.println("2. Emfanisi Stixion Oximatos:");
        System.out.println("3. Lista Theseon Parking");
        System.out.println("4. Telos");
        System.out.print("      Doste epilogi (1-4): ");


        choice=UserInput.getInteger();

            menu:{
        if(choice==1){
            boolean flag=false;

            for(int i=0; i<theseis.length; i++)
                if(theseis[i]==false)
                    flag=true;

            if(flag==false)
                System.out.println("Den uparxei keni thesi");
                

            if(flag==true){
                System.out.print("Sas protinoume autin tin thesi: ");

                int protinomeno_pos;
                protinomeno_pos=MyUtils.protropi(theseis);

                System.out.println(protinomeno_pos+1);

            System.out.println();

            number=counter; 

            System.out.println("Dose arithmo pinakidas: ");
            sign=UserInput.getString();

            System.out.println("Dose ton typo tou autokinitou: ");
            type=UserInput.getString();

            time=MyUtils.findTime();

            System.out.println("Dose thn thesi parking");
            position=UserInput.getInteger();
            position--;
            if(position!=protinomeno_pos)
                if(theseis[position]==true){
                    System.out.println("H thesi den einai keni");
                    break menu;
                }

            if(position>10){
                System.out.println("Lathos arithmos thesis");
                break menu;
            }
            table[position]=new Vehicle(number, sign, type, time, position);

            theseis[position]=true;

            counter++;
            }

        }
            }
        if(choice==2){
            System.out.println("Dialekse tropo anazitisis");
            System.out.println("1. Me bash thn pinakida");
            System.out.println("2. Me bash ton arithmo thesis");

            int choose;
            choose=UserInput.getInteger();

            if(choose==1){
                System.out.println("Dose ton arithmo ths pinakidas");
                String findSign;
                findSign=UserInput.getString();
                int done;
                done=MyUtils.seq_search(table, findSign);

                if(done==-1)
                    System.out.println("To oxima den brethike");
                else{
                    System.out.println("To oxima brethike");
                    MyUtils.printVehicle(done, table);
                }
            }

            if(choose==2){
                System.out.println("Dose ton arithmo thesis");
                int findPosition;
                findPosition=UserInput.getInteger();
                findPosition--;
                int done;
                [B]done=MyUtils.bin_search(table, findPosition);[/B]

                if(done==-1)
                    System.out.println("To oxima den brethike");
                else{
                    System.out.println("To oxima brethike");
                    MyUtils.printVehicle(done, table);
                }
            }
            

        }

        if(choice==3){
            System.out.println("Lista theseon parking:");
            for(int i=0; i<theseis.length; i++){
                if(theseis[i]==true)
                    System.out.println("Thesi "+i+": Kateillhmeni me arithmo pinakidas autokinitou "+table[i].getSign());

                if(theseis[i]==false)
                    System.out.println("Thesi "+i+": Diathesimi");
            }
            
        }

        if(choice==4){
            System.out.println("Telos programmatos");
            menu=true;
            }
        }while(menu==false);

    }
}


// Ekremei to ESC function

I know that some sentences are in greek but thats not a problem.

The error i get is this:
Exception in thread "main" java.lang.NullPointerException
at MyUtils.bin_search(VehicleDemo.java:122)
at VehicleDemo.main(VehicleDemo.java:261)
Java Result: 1
BUILD SUCCESSFUL (total time: 15 seconds)

I bolded the two lines of code. When I give the position of the Vehicle I want to search, it gives me this error message. Because something is going wrong at bin_search().

I would appreciate if you could help me. I use seq_search() to search for a certain Vehicle with a certain position.

Thanks.

EDIT:
Ok, I think I know the problem. It happens with other methods too. Is it because I didnt fill all the Vehicle table[] ??
What can I do to prevent this error to happen, maybe use another constructor?

Thanks.

[pbrockway2]

if(findPosition<table[mid].getPosition())
    right=mid-1;
else if(findPosition>table[mid].getPosition())
    left=mid+1;

Yes - that logic is going to blow up if table[mid] is null. The easiest thing I can think of to fix this is ... not to use an array. If you use a List of some sort like ArrayList<Vehicle> then there are already library methods to search and sort.