Thread: comparing objects using compareTo

Im modeling a car odometer, by making an odometer class, where when the user makes a new odometer(n), n is the number of counters shown. for instance an odometer(6) would be 000000 and the be incremented through the driver program.
My problem is when i get down to the compareTo method, i cant figure out how to compare the parameter object o to an odometer object to determine whether their mileage is less than equal to or greater than the one being compared. My teacher created a driver program to test our classes, and I have everything else working except comparing the objects. any advice would be great.

this is the driver

public class OdometerDriver {
 
	public static void main(String [] args) {
 
		Odometer od6 = new Odometer(), od4 = new Odometer(4);
 
		System.out.println("od6 #1: " + od6);
		System.out.println("od4 #1: " + od4);
 
		for (int i = 1; i <= 21993; i++) {
			od6.inc(); od4.inc();
		}
 
		System.out.println("od6 #2: " + od6);
		System.out.println("od4 #2: " + od4);
		System.out.println("od6 rollovers: " + od6.rollovers());
		System.out.println("od4 rollovers: " + od4.rollovers());
		System.out.println("od4 total mileage: " + od4.totalMileage());
		System.out.println("od4 = od6? " + od4.equals(od6));
		System.out.println("od4.compareTo(od6): "+ od4.compareTo(od6)); od4.inc();
		System.out.println("od4 #3: " + od4);
		System.out.println("od4.compareTo(od6): "+ od4.compareTo(od6));
	}
}

and this is my class

import java.text.*;
public class Odometer implements Comparable{
	int n;
	int miles, totalMiles;
	int rolls;
 
	public Odometer(){
		this.n = 6;
	}
	public Odometer(int n){
		this.n = n;
		if(n < 3 || n > 6){
			System.out.println("N is outside the range. Must be 3 - 6.");
			n = 6;
		}
		miles = 0; rolls = 0; totalMiles = 0;
	}
	public void inc(){
		miles++;
		if(n == 3){
			if(miles > 999){
				miles = 0;
				rolls++;
			}totalMiles = (miles + (rolls * 1000));
		}
		if(n == 4){
			if(miles > 9999){
				miles = 0;
				rolls++;
			}totalMiles = (miles + (rolls * 10000));
		}
		if(n == 5){
			if(miles > 99999){
				miles = 0;
				rolls++;
			}totalMiles = (miles + (rolls * 100000));
		}
		if(n == 6){
			if(miles > 999999){
				miles = 0;
				rolls++;
			}totalMiles = (miles + (rolls * 1000000));
		}
	}
	public int currentMileage(){
		return miles;
	}
	public int totalMileage(){
		return totalMiles;
	}
	public int rollovers(){
		return rolls;
	}
	public String toString(){
		String value = "";
		DecimalFormat df1 = new DecimalFormat("000");
		DecimalFormat df2 = new DecimalFormat("0000");
		DecimalFormat df3 = new DecimalFormat("00000");
		DecimalFormat df4 = new DecimalFormat("000000");
		if(n == 3)
			value = "" + df1.format(miles);
		else if(n == 4)
			value = "" + df2.format(miles) + "";
		else if(n == 5)
			value = "" + df3.format(miles);
		else if(n == 6)
			value = "" + df4.format(miles);
		return value;
	}
	public int compareTo(Object o){
		o = (Odometer)o;
 
		if( == )	
			return 0;
		else if( > )
			return 1;
		else
			return -1;
		// Returns a -1, 0, or 1 as this object is less than, equal to, or
		// greater than the specified object (the formal argument). Comparison
		// made on total mileage.
	}
	public boolean equals(Object odometer){
 
		if( == )
			return true;
		else 
			return false;
 
		// returns true if the total mileage of 2
		// odometers are equal (i.e. including rollovers),
		// false otherwise. Note that odometers of different
		// lengths can be equal, i.e. have the same
		// total mileage
	}
	public boolean hasRolledOver(){
		if(rolls >= 1)
			return true;
		else
			return false;
	}
}