changing properties of item in arraylist

Question

I’m developing a application that will borrow a car to the user, user can choose from the fleet available. Unfortunately when registration number is typed in and name of the borrower is given, program assigns that person to the first entry in arrayList that has been added. I’m not sure how to get program to assign borrower to the item with given registration number. Can anyone point out the mistake I’m making?

Method that sets borrower:

    public void askBorrower(){
    boolean loop = false;
    while(!loop){
        String bName = Console.askString("Borrower's Name: ");
        while(bName.isEmpty()){
            System.out.println("Borrower's name cannot be empty!");
            bName = Console.askString("Borrower's Name: ");
        }
        while(!bName.matches("[a-zA-Z]+")){
            System.out.println("Letters only allowed!");
            bName = Console.askString("Borrower's Name: ");
        }
        setBorrower(bName);
        loop = true;
        boolean newAvailability = false;
        setAvailability(newAvailability);
        System.out.println("You have successfully borrowed a car.");
    }
}

In main class switch triggering borrowing process:

 case 4:
               System.out.println("Borrowing a car:");
               System.out.println("");
               sCar = new StaffCar(); 
               sCar.askRegNo();
               sCar = (StaffCar)fleet2.find(sCar.getRegNo());
               if(sCar == null){
                   System.out.println("Car not in the fleet, please try again");
               }
               else if(sCar.availability == false){
                   System.out.println("Car is out on loan currently");
               }
               else{
                  sCar.askBorrower();
               }
               break;

and find method:

    public StaffCar find(String regNo){ 
    int index = regNo.indexOf(regNo);
    if(index == -1){
        return null;
    }
    else{
        return fleet2.get(index);

    }
}

I would very much appreciate any comments or suggestions.

regNo.indexOf(regNo) will always return 0. You are looking for a string inside itself. — RealSkeptic
– RealSkeptic, Commented Jun 15, 2015 at 20:00

Eran · Accepted Answer · 2015-06-15 20:05:02Z

2

int index = regNo.indexOf(regNo);

Is searching for the registration number in the registration number String, which will always return 0.

You need to search for the registration number in the List. Since fleet2 is a List<StaffCar>, you can't use indexOf(regNo) to locate a car by its registration number. You have to iterate over the List by yourself.

for (StaffCar car : fleet2) {
    if (car.getRegNo().equals(regNo))
        return car;
}
return null;

edited Jun 15, 2015 at 20:05

answered Jun 15, 2015 at 19:58

Eran

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10 Comments

River Over a year ago

Beat me to it =/ This is indeed your problem.

River Over a year ago

Technically if StaffCar only checks for equality based on regNo, fleet2.indexOf(new StaffCar(regNo)); would also work.

Eran Over a year ago

@River No it wouldn't, unless StaffCar's equals may return true when comparing a StaffCar instance to a String instance, which would be strange.

River Over a year ago

Where do you get a String instance from? fleet2 is a list of StaffCar and I'm passing indexOf a StaffCar as well.

Eran Over a year ago

@River Hmm, I didn't notice how find was actually used. You got a point there.

|

Gerald Mücke · Accepted Answer · 2015-06-15 20:04:59Z

1

int index = regNo.indexOf(regNo);

this line will always return 0 because you're querying for the index position of a string in the string itself position of 'dog' in 'dog' is always 0.

Assuming you fleet2 is a List, the indexOf method will only give you the position of the element you're passing as parameter. I.e. indexOf(aStaffCar) will give you the position of the car while indexOf(aString) will always gives you -1. I'd sugest you use a Map<String,StaffCar> with the String regNo being the key.

Map<String,StaffCar> fleet2 = ...,

public StaffCar find(String regNo){ 
  //will return null if no entry with key regNo found
  return fleet2.get(regNo);
}

edited Jun 15, 2015 at 20:04

answered Jun 15, 2015 at 19:59

Gerald Mücke

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1 Comment

River Over a year ago

Love the suggestion for O(1) lookup

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