Question

This code asks user to enter vehicle object that has name, model year, listing price, and percent Discount. The problem that is occurring here, when user enters all of the above info the car object is added to the bottom of the array list and not in the alphabetical order. Note the list was alphabetized before.

while (!valid) {
    String str = scan.nextLine();
    try {
        boolean found = false;
        System.out.println("Enter car name: ");
        name = scan.nextLine();
        System.out.println("Enter car model year: ");
        modelYear = scan.nextLine();
        System.out.println("Enter car list price: ");
        listPrice = scan.nextDouble();
        System.out.println("Enter car percent discount: ");
        percentDiscount = scan.nextDouble();

        int i = 0;
        loc = 0;
        while (!found && i < carList.size()) {
            String nameRetrievedFromCarList = carList.get(i).getName();
            String nameToAdd = "";
            if (nameToAdd.compareToIgnoreCase(nameRetrievedFromCarList) < 0) {
                loc++;
                found = true;

            }
            i++;

        }// end while

        Proj1CarData newCar = new Proj1CarData(name, modelYear, listPrice, percentDiscount,
                discountAmount, netPrice);
        carList.add(loc, newCar);

        valid = true;

    }// end try

    catch (NumberFormatException nfe) {
        System.out.println("Wrong entry:  Try again");
    }// end catch

}

Answer 1

While slightly off topic, you could use Collections.binarySearch to determine where the new value should be inserted…

From the Java Docs

Returns:
the index of the search key, if it is contained in the list; otherwise, (-(insertion point) – 1). The insertion point is defined as
the point at which the key would be inserted into the list: the index
of the first element greater than the key, or list.size() if all
elements in the list are less than the specified key. Note that this
guarantees that the return value will be >= 0 if and only if the key
is found.

Proj1CarData newCar = new Proj1CarData(name, modelYear, listPrice, percentDiscount, discountAmount, netPrice);

int index = Collections.binarySearch(carList, newCar);
if (index < 0) {
    index = (index * -1) - 1;
}

carList.add(index, newCar);

This assumes that Proj1CarData is Comparable, other wise you will need to supply your own Comparator

Proj1CarData newCar = new Proj1CarData(name, modelYear, listPrice, percentDiscount, discountAmount, netPrice);

int index = Collections.binarySearch(carList, newCar, 
    new Comparator<Proj1CarData>() {
        public int compare(Proj1CarData car1, Proj1CarData car2) {
            return car1.getName().compareToIgnoreCase(car2.getName());
        }
    });

if (index < 0) {
    index = (index * -1) - 1;
}

carList.add(index, newCar);

UPDATED

List<String> names = new ArrayList<String>(25);
names.add("Hurzdiirn");
names.add("Alydriira Talabdiira");
names.add("Urlidil Sineth");
names.add("Quavyraen Belarral");
names.add("Belarayne'bryn Agh'Quarbryn");
names.add("Alakgos");
names.add("Sszoj'hrae Laelraema");
names.add("Szornet");
names.add("Filojafay");
names.add("Lltril'net Chaszhrae");

Collections.sort(names);

for (int index = 0; index < names.size(); index++) {
    String name = names.get(index);
    System.out.println("[" + index + "] " + name);
}

int insertAt = Collections.binarySearch(names, "Luke");
if (insertAt < 0) {
    insertAt = (insertAt * -1) - 1;
}

names.add(insertAt, "Luke");

for (int index = 0; index < names.size(); index++) {
    String name = names.get(index);
    System.out.println("[" + index + "] " + name);
}

Collections.sort(names);
for (int index = 0; index < names.size(); index++) {
    String name = names.get(index);
    System.out.println("[" + index + "] " + name);
}