Java Reference
In-Depth Information
Implementing java.lang.Comparable
Another best practice acknowledged by the Java community is to use
java.lang.Comparable
for
comparisons that are “natural” to the object. People naturally sort themselves by name (just look at a
phone book), so it makes sense to implement
java.lang.Comparable
and have its
compareTo
method tell
us whether a name is less than, equal to, or greater than another person's name. Listing 4-30 shows our
Person
class again, with the addition of implementing
java.lang.Comparable
. For our
Person
example,
we get the numeric value of each
String
field, add them together, and use that as the numeric value of
our
Person
object.
Listing 4-30. Person class implementing java.lang.Comparable
package com.apress.javaforabsolutebeginners .examples.comparing;
public class Person implements Comparable<Person> {
String firstName;
String lastName;
public Person (String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
public boolean equals(Person p) {
if (p == null) {
return false;
}
if (p == this) {
return true;
}
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;
}
public int compareTo(Person p) {
int thisTotal = firstName.hashCode() + lastName.hashCode();
int pTotal = p.firstName.hashCode() + p.lastName.hashCode();
if (thisTotal > pTotal) {
