Range

Martin Fowler has written about the [Range Base Pattern] for representing a range of values. Here's a generic base class I wrote in Java which has the same basic functionality. I usually subclass this and add type specific methods.

<geshi lang="java"> /**

* A generic range.  I would prefer to define this as Range<E extends Comparable<? super E>>,
* but then pre 1.5 types can't be used with this.
* Additionally, you run into hell when you have Base implements Comparable<Base> and want to have
* Derived extends Base.  Derived can't implement Comparable<Derived> because it's already defined differently
* in the base class.
*/

public class Range<E extends Comparable> {

   protected final E min;
   protected final E max;

   public Range(E min, E max) {
       GuardHelper.notNullMultiple(min, max);
       validate(min, max);
       this.min = min;
       this.max = max;
   }

   protected void validate(E min, E max) {
       if (min.compareTo(max) > 0) {
           throw new IllegalArgumentException(min + " < " + max);
       }
   }

   public boolean contains(E value) {
       return value != null && min.compareTo(value) <= 0
               && max.compareTo(value) >= 0;
   }

   public E getMinimum() {
       return min;
   }

   public E getMaximum() {
       return max;
   }

   public int hashCode() {
       return min.hashCode() + max.hashCode();
   }

   public boolean equals(Object o) {
       if (this == o) {
           return true;
       }
       if (o == null || getClass() != o.getClass()) {
           return false;
       }

       Range range = (Range) o;

       return max.equals(range.max) && min.equals(range.min);
   }

   @Override
   public String toString() {
       return min + ".." + max;
   }

} </geshi>

And of course the unit test <geshi lang="java"> public class RangeUnitTest extends UnitTestCase {

   public void testContains() {
       Range<Integer> range = new Range<Integer>(3, 5);
       assertFalse(range.contains(2));
       assertTrue(range.contains(3));
       assertTrue(range.contains(4));
       assertTrue(range.contains(5));
       assertFalse(range.contains(6));
   }

   public void testCtor() {
       try {
           new Range<Integer>(5, 3);
           failIfNoExceptionThrown();
       } catch (IllegalArgumentException e) {
           pass();
       }
   }

} </geshi>