23. The Comparable interface

• The Comparable interface is defined in the Java API as follows:

  
      public interface Comparable {
         int compareTo(Object obj);
      }
  
  

• An Item class that implements the Comparable interface:

  
      public class Item implements Comparable {
          private int number;
          private String description;
  
          public Item(int number, String description) {
              this.number = number;
              this.description = description;
          }
  
          public int getNumber() {
              return number;
          }
  
          public String getDescription() {
              return description;
          }
  
          // NOTE: @Override indicates programmer's intention to
          // override a method declared in an interface or a superclass:
          @Override
          public int compareTo(Object o) {
              Item i = (Item) o;
              if (this.getNumber() < i.getNumber())
                  return -1;
              if (this.getNumber() > i.getNumber())
                  return 1;
              return 0;
          }
      }//class Item