Question

I have this class…

public class StartStopTouple {

    public int iStart;
    public int iStop;
    public int iHashCode;

    public StartStopTouple(String start, String stop) {
        this.iStart = Integer.parseInt(start);
        this.iStop = Integer.parseInt(stop);
    }

    @Override
    public boolean equals(Object theObject) {

        // check if 'theObject' is null
        if (theObject == null) {
            return false;
        }
        // check if 'theObject' is a reference to 'this' StartStopTouple... essentially they are the same Object
        if (this == theObject) {
            return true;
        }

        // check if 'theObject' is of the correct type as 'this' StartStopTouple
        if (!(theObject instanceof StartStopTouple)) {
            return false;
        }

        // cast 'theObject' to the correct type: StartStopTouple
        StartStopTouple theSST = (StartStopTouple) theObject;

        // check if the (start,stop) pairs match, then the 'theObject' is equal to 'this' Object
        if (this.iStart == theSST.iStart && this.iStop == theSST.iStop) {
            return true;
        } else {
            return false;
        }
    } // equal() end

    @Override
    public int hashCode() {
        return iHashCode;
    }
}

… and I define equality between such Objects only if iStart and iStop in one Object are equal to iStart and iStop in the other Object.

So since I’ve overridden equals(), I need to override hashCode() but I’m not sure how to define a good hash function for this class. What would be a good way to create a hash code for this class using iStart and iStop?

Answer 1

I’d be tempted to use this, particularly since you’re going to memoize it:

Long.valueOf((((long) iStart) << 32) | istop)).hashcode();