Question

This is what I’m trying to do: I’m reading a file in from the command line. The file contains a list of data,below this paragraph is what it looks like. The problem I’m having is with the if statements.

import java.util.*; import java.io.*;  public class VehicleTest {     public static void main(String[] args) throws FileNotFoundException {         String vehicle = 'vehicle';         String car = 'car';         String americanCar = 'american car';         String foreignCar = 'foreign car';         String truck = 'truck';         String bicycle = 'bicycle';          File file = new File(args[0]);         Scanner input = new Scanner(file);          String[] autos = new String[100];         ArrayList allVehicles = new ArrayList();           for (int i = 0; i < autos.length; i++) {             autos[i] = input.nextLine();         }          int j = 0;         int i = 0;          while (i++ < autos.length) {             if (vehicle.equalsIgnoreCase(autos[j++])) {                 Vehicle v = new Vehicle();                 v.setOwnerName(autos[j]);                 allVehicles.add(v);             }else if(car.equalsIgnoreCase(autos[j++])){                 Car c = new Car();                 c.setOwnerName(autos[j]);                 allVehicles.add(c);             }         }          for(Object a: allVehicles){             System.out.println(a);         }     } } 

In pseudo code this would be:

while i is less than the length of the string  array    if you see the word vehicle create a new vehicle object and add it to the arrayList.    if you see the word car create a new car object and add it to the arrayList.   ..... 

The problems is that I get an arrayOutOfBounds exception with the code I’m using.

I understand that j++ is what is wrong, but how else am I supposed to iterate through the string array so that I can read each line and create the appropriate objects? I’m at a loss as to what to do. I need some help.

foreign car   aMarioy   Mario's house   [phone]   [e-mail]   false   black   Italy   4415.91    truck   aDougy   Doug's house   [phone]   [e-mail]   30   61234.56   8/10/2003    vehicle   aRobby   Rob's house   [phone]   [e-mail]    bicycle   bTommy   Tom's house   [phone]   [e-mail]   7    truck   bGeorge   George's house   [phone]   [e-mail]   25   51234.56   12/4/2004    vehicle   bTim   Tim's house   [phone]   [e-mail]    bicycle   bJim   Jim's house   [phone]   [e-mail]   5    american car   bJohn   John's house   [phone]   [e-mail]   true   green   false   true    car   cKen   Ken's house   [phone]   [e-mail]   false   orange    foreign car   cMario   Mario's house   [phone]   [e-mail]   false   black   Italy   4415.91     american car   gSam   Sam's house   [phone]   [e-mail]   false   blue   true   false   

Answer 1

A couple of problems:

• You’re incrementing j in both ‘if’ tests. I haven’t checked to be certain (it’s quite convoluted code, to be honest) but if you make sure that you only increment j when you’ve found a match, that will help.
• Your test using i basically means it will try to read as many vehicles as there are lines in the file, rather than stopping when you’ve reached the end of the file. Basically you don’t need i here.

Here’s one changed version:

    while (j < autos.length) {         if (vehicle.equalsIgnoreCase(autos[j])) {             j++;             Vehicle v = new Vehicle();             v.setOwnerName(autos[j++]);             allVehicles.add(v);         } else if(car.equalsIgnoreCase(autos[j])){             j++;             Car c = new Car();             c.setOwnerName(autos[j++]);             allVehicles.add(c);         }     } 

It would be slightly cleaner to extract the type once though – then you can do the comparisons separately:

    while (j < autos.length) {         String type = autos[j++];         if (vehicle.equalsIgnoreCase(type)) {             Vehicle v = new Vehicle();             v.setOwnerName(autos[j++]);             allVehicles.add(v);         } else if(car.equalsIgnoreCase(type)){             Car c = new Car();             c.setOwnerName(autos[j++]);             allVehicles.add(c);         }     } 

It’s still not quite how I’d do it, but it’s closer…

My next step would be to use the scanner more appropriately:

while (scanner.hasNext()) {     String type = scanner.nextLine();     if (type.equalsIgnoreCase('vehicle')) {         allVehicles.add(new Vehicle(scanner));     } else if (type.equalsIgnoreCase('car')) {         allVehicles.add(new Car(scanner));     }     // ... } 

Then make the constructor for Vehicle, Car etc do the parsing directly from the scanner.

The next step would be to separate out the construction from the iteration. Introduce a new method:

// Use a base type in real code private static Object parseNextVehicle(Scanner scanner) {     String type = scanner.nextLine();     if (type.equalsIgnoreCase('vehicle')) {         return new Vehicle(scanner);     } else if (type.equalsIgnoreCase('car')) {         return new Car(scanner);     }     // ... throw an exception indicating an unknown vehicle type }  // ... and then in the main method, use it like this: while (scanner.hasNextLine()) {     allVehicles.add(parseNextVehicle(scanner)); }