AP Computer Science --- Haas --- ComparableInterface

The examples below show how objects which are Comparable can use the sort method in the array class.

/**
 * This example String objects in an array get sorted.
 */
import java.util.Arrays;

public class SortingStrings
{  
   public static void main(String[] args)
   {
     String animals[] = new String[4];
     animals[0] = "weasel";
     animals[1] = "kangaroo";
     animals[2] = "aardvark";
     animals[3] = "chipmunk";

     for (int i=0; i<4; i++) {
       System.out.println("animal " + i + " : " + animals[i]);
     }

     /***
      * The method sort is in the Array class.  The sort method can sort
      * any set of objects that implements the Comparable interface by
      * having a compareTo method.
      * 
      * Strings can be sorted since they are Comparable.
      */
     Arrays.sort(animals);

     for (int i=0; i<4; i++) {
       System.out.println("animal " + i + " : " + animals[i]);
      }
    }
}

A second example...

/**
 * This example shows sorting of an array of Person objects.
 * Make sure you understand how it works.
 */
public class Person implements Comparable {
  private String firstName;
  private String lastName;
  private int age;
  
  public Person(String first, String last, int ageOf)  {
      firstName = first;
      lastName = last;
      age = ageOf;
  }
  
  public String getFirstName() {
    return firstName;
  }

  public String getLastName() {
    return lastName;
  }

  public int getAge() {
    return age;
  }
  
  public void printPerson() {
      System.out.println(firstName + ", " + lastName + ", " + age);
  }
  
  public int compareTo(Object anotherPerson) {
      // Note that anotherPerson must be cast as a Person in order to 
      // use the method getLastName.
      String otherLast = ((Person)anotherPerson).getLastName();

      // uses the compareTo method in the String class
      return lastName.compareTo(otherLast);
  }
}

import java.util.Arrays;
/**
 * Note that the array of type Person is able to be sorted
 * because Person implements the Comparable interface.
 */
public class SortingPeople 
{  
   public static void main(String[] args)
   {
     Person[] persons = new Person[6];
     persons[0] = new Person("Art", "Vandelay", 56);
     persons[1] = new Person("Carl", "Farbman", 45);
     persons[2] = new Person("Dr.", "VanNostrand", 48);
     persons[3] = new Person("Joe", "Divola", 50);
     persons[4] = new Person("Izzy", "Mandelbaum", 75);
     persons[5] = new Person("Jackie", "Chiles", 49);
            
     System.out.println("\nBefore Sort ...");
     
     for (int i=0; i< persons.length; i++) {
       persons[i].printPerson();
     }
    
     Arrays.sort(persons);

     System.out.println("\nAfter Sort ...");

     for (int i=0; i< persons.length; i++) {
       persons[i].printPerson();
     }
  }
}