Operators - Java 7 for Absolute Beginners - page 66

if (!(p instanceof Person)) {
return false;
}
if (p.lastName.equals(this.lastName)
&& p.firstName.equals(this.firstName)) {
return true;
} else {
return false;
}
}
public int hashCode() {
int result = 17;
result *= firstName.hashCode() * 37;
result *= lastName.hashCode() * 37;
return result;
}
}
Let's examine that equals method. I followed a standard recipe for implementing it. (The Java
community has best practices for many things, and we show them to you whenever they come up, as
here.) First, I check for null, just to make sure we have an object. Then I check to see whether it's the
same object, in which case they are certainly equal. Then we check to make sure that, if we do have an
object, it's a Person object. If not, the comparison is always false. But remember that other classes might
extend our Person class, so a Student object might be equal to our Person object. Because Student
extends Person , this equals method works for both. However, Student might implement its own equals
method to account for the school each student attends. Finally, I check all the relevant fields within the
class. If they are all equal, it must be the same person. Naturally, a real-world Person class probably
includes middle name, address fields, social security number, and possibly even ancestors and
descendants. Two fields will do for the sake of a demonstration, though. Now, let's rewrite CompareTest
to use our new Person object (see Listing 4-29).
Listing 4-29. Checking people objects for equality
package com.apress.javaforabsolutebeginners .examples.comparing;
public class CompareTest {
public static void main(String[] args) {
Person samSpade = new Person("Sam", "Spade");
Person greatNoirDetective = new Person("Sam", "Spade");
System.out.println(samSpade == greatNoirDetective);
System.out.println(samSpade.equals(greatNoirDetective));
}
}
CompareTest now prints “false” and then “true,” even though samSpade and greatNoirDetective are
different references to different Person objects. That's because our equals method isn't comparing
references but rather the relevant fields of the two objects.