Fundamentals - SCJP Sun Certified Programmer for Java Platform SE6 - page 59

Let's look at an example. Suppose we have the following class named Dog :
1. public class Dog {
2. private String name;
3. private int age;
4.
5. public Dog(String name, int age) {
6. this.name = name;
7. this.age = age;
8. }
9. }
What does it mean for two Dog objects to be equal? Suppose in our application two Dog
objects are equal if they have the same name and age. Then Dog can override equals and
implement this business logic:
1. public class Dog {
2. private String name;
3. private int age;
4.
5. public Dog(String name, int age) {
6. this.name = name;
7. this.age = age;
8. }
9.
10. public boolean equals(Object obj) {
11. if(!(obj instanceof Dog))
12. return false;
13. Dog other = (Dog) obj;
14. if(this.name.equals(other.name) &&
15. (this.age == other.age)) {
16. return true;
17. } else {
18. return false;
19. }
20. }
21. }
Within equals , we fi rst test to see if the class type of the other object is Dog . If the other
object is not a Dog object, we can quickly deduce the two objects are not equal. Otherwise,
the incoming reference is cast to a Dog reference and the name and age are checked for
equality. Because the name is a String object, we use the equals method of the String class
to compare the two name objects.