java11-collections-sortedset-subset-methods

preface

• interface SortedSet<E> extends Set<E>
• class TreeSet<E> implements SortedSet<E>
• the implementation class for SortedSet should have a constructor accepting Comparator
• if no comparator is specified it should use natural ordering (compareTo() method of elements to sort them)
• if a class does not implements Comparable and we will not specify Comparator then ClassCastException is thrown while attempting to add element
• handling null:
  • NullPointerException in case of natural order
  • depends on Comparator

subset methods

• SortedSet<E> subSet(E inclusive, E exclusive)
  • returns a view of this set - [inclusive, exclusive)
  • changes in the returned set are reflected in this set, and vice-versa
  • IllegalArgumentException
    • if fromElement > toElement
    • on an attempt to insert an element outside its range
  • ClassCastException if E does not implement Comparable and we don't specify set's Comparator
• SortedSet<E> headSet(E exclusive)
  • returns a view of this set - [beginning, exclusive)
  • changes in the returned set are reflected in this set, and vice-versa
  • IllegalArgumentException - on an attempt to insert an element outside its range
  • ClassCastException if E does not implement Comparable and we don't specify set's Comparator
• SortedSet<E> tailSet(E inclusive)
  • similar to headSet
• E first()
• E last()

project description

We will show basic tests of mentioned above subset methods:

1. subset
   • create subset

     SortedSet<Integer> integers = new TreeSet<>(Arrays.asList(1, 2, 3));
     
     var subset = integers.subSet(0, 20);
     
     assertEquals(Set.of(1, 2, 3), subset);
     

   • if we modify the subset the source is modified as well

     SortedSet<Integer> integers = new TreeSet<>(Arrays.asList(1, 2, 3));
     
     var subset = integers.subSet(2, 5); [2, 3]
     subset.add(4);
     
     assertEquals(Set.of(2, 3, 4), subset);
     assertEquals(Set.of(1, 2, 3, 4), integers);
     

   • if we modify the source the subset is modified as well

     SortedSet<Integer> integers = new TreeSet<>(Arrays.asList(1, 2, 3));
     
     var subset = integers.subSet(2, 5); [2, 3]
     integers.add(4);
     
     assertEquals(Set.of(2, 3, 4), subset);
     assertEquals(Set.of(1, 2, 3, 4), integers);
     

   • inserting out of range will throw IllegalArgumentException

     @Test(expected = IllegalArgumentException.class)
     public void subset_modify_outOfRange() {
         SortedSet<Integer> integers = new TreeSet<>(Arrays.asList(1, 2, 3));
     
         var subset = integers.subSet(2, 4);
         subset.add(4);
     }
     

2. headSet
   • create headSet

     SortedSet<Integer> integers = new TreeSet<>(Arrays.asList(1, 2, 3));
     
     var headSet = integers.headSet(3);
     
     assertEquals(Set.of(1, 2), headSet);
     

   • toElement > range

     SortedSet<Integer> integers = new TreeSet<>(Arrays.asList(1, 2, 3));
     
     var headSet = integers.headSet(4);
     
     assertEquals(Set.of(1, 2, 3), headSet);
     

   • toElement < beginning

     SortedSet<Integer> integers = new TreeSet<>(Arrays.asList(1, 2, 3));
     
     var headSet = integers.headSet(0);
     
     assertThat(headSet, is(empty()));
     

   • if we modify the headSet the source is also modified

     SortedSet<Integer> integers = new TreeSet<>(Arrays.asList(1, 3));
     
     var headSet = integers.headSet(3); // [1]
     integers.add(2);
     
     assertEquals(Set.of(1, 2), headSet);
     assertEquals(Set.of(1, 2, 3), integers);
     

   • if we modify the source the headSet is also modified

     SortedSet<Integer> integers = new TreeSet<>(Arrays.asList(1, 3));
     
     var headSet = integers.headSet(3); // [1]
     integers.add(2);
     
     assertEquals(Set.of(1, 2), headSet);
     assertEquals(Set.of(1, 2, 3), integers);      
     

   • inserting out of range will throw IllegalArgumentException

     @Test(expected = IllegalArgumentException.class)
     public void headSet_modify_outOfRange() {
         SortedSet<Integer> integers = new TreeSet<>(Arrays.asList(1, 2, 3));
     
         var headSet = integers.headSet(4);
         headSet.add(4);
     }
     

3. tailSet - similar to headSet
4. first / last

   assertThat(new TreeSet<>(Arrays.asList(1, 2, 3)).first(), is(1));
   

   assertThat(new TreeSet<>(Arrays.asList(1, 2, 3)).last(), is(3));