Sorting a Vector of custom-made classes.

Question

Hi,
I have a class Car which has the following private members:
Strings year, make, model, engine and transmission.
I have another class CarList which extends Vector (a vector of Car objects).
I wish to create a method called "sortCarList()" in class CarList which will sort all of the Car objects in the vector first by "year", then by "make", then by "model". I am using a bubble sort. I tried simply sorting the Car objects in CarList by year using the "compareTo()" method. The comparison works fine, but the actual re-arranging of elements is causing me grief. Here's my current code for the "sortCarList()" method in vector class CarList:
public void sortCarList() {
for (int i = 0; i < (size() - 1); i++) {
for( int j = 0; i < (size() - 1); i++)     {
     if (elementAt(j).getYear().compareTo(elementAt(j + 1).getYear()) > 0) {
Car tempHolder;
     tempHolder = elementAt(j);
          elementAt(j) = elementAt(j + 1);
          elementAt(j + 1) = tempHolder;
I'm getting the error (NetBeans):
(Unexpected type)
required: variable
found : value
elementAt(j) = elementAt(j + 1);
--------------^
- and -
required: variable
found : value
elementAt(j + 1) = tempHolder;
--------------^
So I'm just getting the error because the way I'm trying to switch the vector elements with one another! I haven't coded in Java for a while and have since spent a college semester programming in COBOL so my reality is a bit fuddled. Is this a reference problem? Or is there something else I'm just not catching here? Help would be very appreciated!
After I get this first simple issue out of the way, I can then start implementing a more complex sort which also takes MAKE and MODEL into consideration.
So in the end I'm looking for this kind of sorting (fields separated for clarity):
YEAR-MAKE-MODEL
1969-Dodge-Super Bee
1969-Plymouth-Road Runner
1969-Pontiac-GTO
1970-Buick-GSX
1970-Chevrolet-Chevelle
As you can see, I want the first order of sorting to be YEAR, then MAKE, then MODEL, which I assume will be a pain to do (if element 0's MODEL value lexicographically higher in the alphabet than element 1's MODEL value, it shouldn't bother sorting them because the MAKES are already in proper order).
Message was edited by:
incogx
Message was edited by:
incogx
Message was edited by:
incogx

Answer 1

Here is an example of a Car class that implements the Comparable interface, and allows Cars to be sorted
by year, make, and model. Since what needs to be sorted are an Integer (year) and Strings (make and model)
which already implement the Comparable interface, this then allows a natural-order comparison to be made
on Cars. This comparison is implemented in the compareTo method at the bottom of the class.
There is a demo program that creates some Car data, sorts it, and prints it out. The sorting is the only
important statement; the rest of the code is for demonstration purposes only.
(The code is an adaption of an example in the Java Tutorial,
http://java.sun.com/docs/books/tutorial/collections/interfaces/order.html
The tutorial has an explanation of some of the code, and is worth reading.)
HTH
import java.util.*;
public class Car implements Comparable<Car>
    private final Integer year;
    private final String make, model;
    public Car(Integer year, String make, String model)
        if (year == null || make == null || model == null)
            throw new NullPointerException();
        this.year = year;
        this.make = make;
        this.model = model;
    public int hashCode()
        return 255*year.hashCode() + 31*make.hashCode() + model.hashCode();
    public String toString()
        return year + " " + make + " " + model;
    public int compareTo(Car n)
        int lastCmp = year.compareTo(n.year);
        int nextCmp = make.compareTo(n.make);
        return (lastCmp != 0 ? lastCmp :
            nextCmp != 0 ? nextCmp :
                model.compareTo(n.model));
import java.util.*;
public class CarSort
    public static void main(String[] args)
        // This creates an array of 6 Car instances
        Car nameArray[] = {
            new Car(1969, "Dodge", "Super Bee"),
            new Car(1970, "Buick", "Roadmaster"),
            new Car(1969, "Pontiac", "GTO"),
            new Car(1970, "Chevrolet", "Chevelle"),
            new Car(1970, "Buick", "GSX"),
            new Car(1969, "Plymouth", "Road Runner")
        // And this loads the Cars into a List
        List<Car> names = Arrays.asList(nameArray);
        // The 2 prior statements just create some data for this demo program
        Collections.sort(names);
        System.out.println(names);
}