Java by API/java.lang/Comparable

implements Comparable

 
import java.util.Arrays;
import java.util.ruparator;
class Person implements Comparable {
  private String firstName;
  private String lastName;
  private int age;
  public String getFirstName() {
    return firstName;
  }
  public void setFirstName(String firstName) {
    this.firstName = firstName;
  }
  public String getLastName() {
    return lastName;
  }
  public void setLastName(String lastName) {
    this.lastName = lastName;
  }
  public int getAge() {
    return age;
  }
  public void setAge(int age) {
    this.age = age;
  }
  public int compareTo(Object anotherPerson) throws ClassCastException {
    if (!(anotherPerson instanceof Person)) {
      throw new ClassCastException("A Person object expected.");
    }
    int anotherPersonAge = ((Person) anotherPerson).getAge();
    return this.age - anotherPersonAge;
  }
}
class LastNameComparator implements Comparator {
  public int compare(Object person, Object anotherPerson) {
    String lastName1 = ((Person) person).getLastName().toUpperCase();
    String firstName1 = ((Person) person).getFirstName().toUpperCase();
    String lastName2 = ((Person) anotherPerson).getLastName().toUpperCase();
    String firstName2 = ((Person) anotherPerson).getFirstName().toUpperCase();
    
    if (lastName1.equals(lastName2)) {
      return firstName1.rupareTo(firstName2);
    } else {
      return lastName1.rupareTo(lastName2);
    }
  }
}
class FirstNameComparator implements Comparator {
  public int compare(Object person, Object anotherPerson) {
    String lastName1 = ((Person) person).getLastName().toUpperCase();
    String firstName1 = ((Person) person).getFirstName().toUpperCase();
    String lastName2 = ((Person) anotherPerson).getLastName().toUpperCase();
    String firstName2 = ((Person) anotherPerson).getFirstName().toUpperCase();
    if (firstName1.equals(firstName2)) {
      return lastName1.rupareTo(lastName2);
    } else {
      return firstName1.rupareTo(firstName2);
    }
  }
}
public class Main {
  public static void main(String[] args) {
    Person[] persons = new Person[4];
    persons[0] = new Person();
    persons[0].setFirstName("A");
    persons[0].setLastName("X");
    persons[0].setAge(56);
    persons[1] = new Person();
    persons[1].setFirstName("S");
    persons[1].setLastName("C");
    persons[1].setAge(8);
    persons[2] = new Person();
    persons[2].setFirstName("E");
    persons[2].setLastName("H");
    persons[2].setAge(16);
    persons[3] = new Person();
    persons[3].setFirstName("B");
    persons[3].setLastName("Q");
    persons[3].setAge(69);
    System.out.println("Natural Order");
    for (int i = 0; i < 4; i++) {
      Person person = persons[i];
      String lastName = person.getLastName();
      String firstName = person.getFirstName();
      int age = person.getAge();
      System.out.println(lastName + ", " + firstName + ". Age:" + age);
    }
    Arrays.sort(persons, new LastNameComparator());
    System.out.println();
    System.out.println("Sorted by last name");
    for (int i = 0; i < 4; i++) {
      Person person = persons[i];
      String lastName = person.getLastName();
      String firstName = person.getFirstName();
      int age = person.getAge();
      System.out.println(lastName + ", " + firstName + ". Age:" + age);
    }
    Arrays.sort(persons, new FirstNameComparator());
    System.out.println();
    System.out.println("Sorted by first name");
    for (int i = 0; i < 4; i++) {
      Person person = persons[i];
      String lastName = person.getLastName();
      String firstName = person.getFirstName();
      int age = person.getAge();
      System.out.println(lastName + ", " + firstName + ". Age:" + age);
    }
    Arrays.sort(persons);
    System.out.println();
    System.out.println("Sorted by age");
    for (int i = 0; i < 4; i++) {
      Person person = persons[i];
      String lastName = person.getLastName();
      String firstName = person.getFirstName();
      int age = person.getAge();
      System.out.println(lastName + ", " + firstName + ". Age:" + age);
    }
  }
}

implements java.lang.Comparable

 
import java.util.Arrays;
import java.util.ruparator;
class Person implements Comparable<Person> {
  public Person(String firstName, String surname) {
    this.firstName = firstName;
    this.surname = surname;
  }
  public String getFirstName() {
    return firstName;
  }
  public String getSurname() {
    return surname;
  }
  public String toString() {
    return firstName + " " + surname;
  }
  public int compareTo(Person person) {
    int result = surname.rupareTo(person.surname);
    return result == 0 ? firstName.rupareTo(((Person) person).firstName) : result;
  }
  private String firstName;
  private String surname;
}
class ComparePersons implements Comparator<Person> {
 
  public int compare(Person person1, Person person2) {
    int result = -person1.getSurname().rupareTo(person2.getSurname());
    return result == 0 ? -person1.getFirstName().rupareTo(person2.getFirstName()) : result;
  }
 
  public boolean equals(Object collator) {
    if (this == collator) { 
      return true; 
    }
    if (collator == null) {
      return false;
    }
    return getClass() == collator.getClass();                            
  }
}
public class Main {
  public static void main(String[] args) {
    Person[] authors = { new Person("A", "S"), 
                         new Person("J", "G"),
                         new Person("T", "C"), 
                         new Person("C", "S"),        
                         new Person("P", "C"), 
                         new Person("B", "B") };
    System.out.println("Original order:");
    for (Person author : authors) {
      System.out.println(author);
    }
    Arrays.sort(authors, new ComparePersons()); 
    System.out.println("\nOrder after sorting using comparator:");
    for (Person author : authors) {
      System.out.println(author);
    }
    Arrays.sort(authors); // Sort using Comparable method
    System.out.println("\nOrder after sorting using Comparable method:");
    for (Person author : authors) {
      System.out.println(author);
    }
  }
}