需要帮助，尝试读取文件并使用Java中的参数填充对象数组

Question

To let you know this is an assignment for my class, I'm just asking for a little help with it. The short form of the assignment is to:

Write an application class that reads a file (from the command line) and fills an array of type vehicle[] with new vehicle (params), new car (params), new american car (params) new foreign car(params) , new truck (params), new bicycle (params), etc.

This is what I have so far(I have already written individual classes for each of the objects that all extend vehicle):

  public class n01029506{
  public static void main(String[] args) throws FileNotFoundException{   
     Scanner input = new Scanner(new File(args[0]));
     ArrayList<Vehicle> list = new ArrayList<>();

  while(input.hasNext()){
     if(input.nextLine().equals("vehicle")){
        String name = input.nextLine();
        String address = input.nextLine();
        String phone = input.nextLine();
        String email = input.nextLine();       
        list.add(new Vehicle(name, address, phone, email));
     }
    }
    System.out.println(list.get(0));
   }
  }

The output of this code is an array of objects called vehicle from the file I am reading. The problem I am having is when I add another else if statement it compiles but I get a runtime error.

     if(input.nextLine().equals("vehicle")){
        String name = input.nextLine();
        String address = input.nextLine();
        String phone = input.nextLine();
        String email = input.nextLine();       
        list.add(new Vehicle(name, address, phone, email));
     }else if(input.nextLine().equals("car")){
        String name = input.nextLine();
        String address = input.nextLine();
        String phone = input.nextLine();
        String email = input.nextLine();    
        boolean convert = input.nextBoolean();
        String color = input.nextLine();   
        list.add(new Car(name, address, phone, email, convert, color));
     }

What I need the program to do is go through and once it reads a line from the file - whether a car, vehicle, etc - it creates and object and stores it in the array. I'm not sure how to get the program to work properly. If anyone could help me in the right direction I would really appreciate it.

Answer 1

I will try to spell out what JB Nizet said in the comment. Assume your input file contains:

car
Riley Clark
3476 9th Ave N
555-555-1234
rc@toyota.jp
false
blue

OK? Now your program reads the line car and compares it to vehicle . Since they are not the same, it goes into the else if part. This will read the line Riley Clark and compare it to car . They are not the same either. So you program will never discover there's a car in these lines of the file.

JB Nizet also gave the solution: “Call nextLine() once , store the result in a variable, and compare this variable with "vehicle", "car", etc.”