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.

score 2 · Accepted Answer · answered Sep 10 '13 at 15:31

2

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.
    }
}

answered Sep 10 '13 at 15:31

Rohit Jain

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Ok so doing it this way I need to override the equals? – user2745043 Sep 10 '13 at 15:40
@user2745043. No. You are comparing strings using equals. – Rohit Jain Sep 10 '13 at 15:41
Being that my sales are of type double would simply casting something like if (this.getState().equals(that.getState())) { return (int) (that.sales - this.sales); be the correct way to do it? – user2745043 Sep 10 '13 at 15:54
@user2745043. No that won't be. Better to return value based on actual comparison result. Use `<`, and `>` for comparison. – Rohit Jain Sep 10 '13 at 15:57
I updated my code using your suggestion for the sales. However, i'm having trouble with the state. It doesn't let me use < or > when comparing them or -. Do I need to check sales using .equals here or is there something else i'm doing wrong? Thanks for all your help by the way. – user2745043 Sep 10 '13 at 16:10
Ok what do you expect this `if (this.sales < that.sales);` to do? You should at least do something in the `if` block. Perhaps `return 1;`. – Rohit Jain Sep 10 '13 at 16:13
Also note that String implements Comparable and you've also got `Double.compare`, so you could just substitute the logic with something like `return state.compareTo(that.state) - Double.compare(sales, that.sales);` and I don't think you'd have to worry about overflows in this case. – sgbj Sep 10 '13 at 16:18
@Rohit Jain. I fixed my code to your suggestion and looked over it a while, does it look like something like this would work without error? Mainly does it seem logically correct? – user2745043 Sep 10 '13 at 21:48

score 0 · Answer 2 · answered Sep 10 '13 at 15:28

0

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.

answered Sep 10 '13 at 15:28

Juned Ahsan

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score 0 · Answer 3 · answered Sep 10 '13 at 15:30

0

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)

answered Sep 10 '13 at 15:30

Moritz Petersen

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compareTo based on two values of objects

3 Answers3