gistfile1.java

class Appointment implements Comparable {

    LocalDateTime time
    String description
    String place

    // Define a natural ordering of Appointments
    // base on their times.
    int compareTo(that) { this.date <=> that.date }

    // Instances should be considered equal if they
    // have equal state
    @Override boolean equals(that) {
        if (this.is(that)) return true
        if (!(this instanceof that)) return false
        this.time == that.time &&
        this.description == that.description &&
        this.place == than.place
    }

    /* ... */

}

def appt = new Appointment(
    time: new LocalDateTime(2010, 5, 4, 15, 0),
    description: "Pain",
    place: "Dental Clinic"
)

def duplicateAppt = new Appointment(
    time: new LocalDateTime(2010, 5, 4, 15, 0),
    description: "Pain",
    place: "Dental Clinic"
)

assert appt == duplicateAppt

duplicateAppt.place = "Torture Chamber"

assert !appt.equals(duplicateAppt)

assert appt != duplicateAppt   // Uh-oh... FAIL!

// This last assertion fails, since under the hood
// Groovy is executing something like
// assert !(appt.compareTo(duplicateAppt) == 0)
// even though it is clear from our class definition
// that the intention is for these objects to be
// considered un-equal.