compareTo based on two values of objects

Question

I'm working on a 'Franchise' program which has a owner, state, and sales, that are all set in the constructor and can't be changed. My problem comes when I'm trying to write my compareTo method.

package prob2;

public class Franchise implements Comparable <Franchise>  {
    final String owner;
    final String state;
    final double sales;

protected Franchise(String owner, String state, double sales ) {
    this.owner = owner;
    this.state = state;
    this.sales = sales;
}

public String toString() {
    String str = state + ", " + sales + ", " + owner;
    return str;
}

public String getState() {
    return state;
}

public double getSales() {
    return sales;
}
public int compareTo(Franchise that) {
    double thatSales = that.getSales();
    if (this.getState().compareTo(that.getState()) <0) 
        return -1;
    else if (this.getSales() > thatSales)
        return -1;
    else if (this.getSales() < thatSales)
        return 1;
    else
        return 0;
}

The program should implement the comparable interface and should compare Franchise objects based on BOTH state ASCENDING and sales DESCENDING. My question is how would I compare using both of the values, is there a way to do it in a single compare, or do i need multiple compareators?

EXAMPLE:

state = CA, sales = 3300 compared to state = NC, sales = 9900 would return NEGATIVE

state = CA, sales = 3300 compared to state = CA, sales = 1000 would return NEGATIVE

state = CA, sales = 3300 compared to state = CA, sales = 9900 would return POSITIVE

Thanks for any and all help.

Answer 1

is there a way to do it in a single compare, or do i need multiple compareators?

In your case, you don't need multiple comparators. Just write the logic based on both the attributes, in single compareTo method, along the lines of:

public int compareTo(Franchise that) {
    if (this.getState().equals(that.getState()) {
        // Compare on the basis of sales (Take care of order - it's descending here)
    } else {
        // Compare on the basis of states.
    }
}

Answer 2

You need to create different comparators by implementing Comparator interface. Depending on the sort param you need to use the appropriate comparator class in Collections.sort method.

Answer 3

Of course you can use only one compare method, in pseudo-code:

lessThan(this.state, a.state) && this.sales > a.sales

(or something like that)