Steven Yong's Weblog

/*
  Person.java
  Created on December 22, 2005, 9:00 PM
*/
import static java.lang.System.out; // 1) Static import

@Pojo ("person") // 2) Annotation (metadata)
public class Person {
  Gender gender; // 3) Type-safe enumeration  
  String firstName;
  String lastName;

  public Person(String firstName, String lastName, Gender gender) {
    this.firstName = firstName;
    this.lastName = lastName;
    this.gender = gender;
    assert(gender != Gender.NEUTRAL); // Assertion J2SE 1.4
  }

  public void join(Group<Person> g) {
    g.add(this);
  }

  public static void main(String[] args) {
    Person p = new Person("Faye", "Wong", Gender.FEMALE);
    Group<Person> personGroup = new Group<Person>(); // 4) Generics
    p.join(personGroup);

    // 5) Varargs
    personGroup.printMemberInfo(p.firstName, p.lastName, p.gender.alias);

    // Ermmm... don't think I want to expose my last name
    personGroup.printMemberInfo(p.firstName, p.gender.alias);

    if (p.getClass().isAnnotationPresent(Pojo.class)) {
      out.println("Reference p is a POJO");
    }

    Group<Integer> integerGroup = new Group<Integer>();
    integerGroup.add(18); // 6) Auto-boxing
    integerGroup.add(new Integer(8)); // Prior J2SE 5.0
  }
}

// Enum Type
enum Gender {
  MALE("M"), FEMALE("F"), NEUTRAL("N");

  String alias;

  Gender(String s) { alias = s; }
}

// Annotation Type
@Retention (RetentionPolicy.RUNTIME)
@Target (ElementType.TYPE)
@interface Pojo { String value() default "undefined"; }

// Generic Type
class Group<E> {
  List<E> members = new ArrayList<E>();

  public Group() {}
  public void add(E e) { members.add(e); }
  public E leave(int index) { return members.remove(index); }
  public List<E>getMembers() { return members; }

  public static void printMemberInfo(String... info) {
    for (String s : info) { // 7) Enhanced for loop
      out.println(s);
    }
  }
}