Java Set Collection: My Review

I'm almost done these but if it helps others to understand what's going on then they'll have been worthwhile. I believe they're helping me :)

• Sets are the collection interface that represents a list of unique values. It can take a list with repeated values and take out repeated data. A list that pulls in unique values.

• A hash is a way to uniquely identify objects.

• In Java every object has a method called hashCode() which is a 32-bit signed integer which can be overridden.

• Several implementatons of Sets exist in Java including.

  • Set
  • SortedSet
  • TreeSet
  • HashSet

Set<String> (set of strings) nameOfSet = new HashSet<String>

• Sets and Lists can interact. You can quickly change the implementation of one Collection to another.

Set<String> uniqueLanguages = new HashSet<String>(allLanguages);
   removes duplicate entries in a given list.

Set<String> uniqueLanguages = new TreeSet<String>(allLanguages);  e.g. Hashsets can become TreeSets which sort automatically.

• Requires import of java.util.Set and java.util.HashSet

• Hashes. A Hash is a way to uniquely identify objects.

• Set<String> - set of strings

Set<String> names = new HashSet<String>();


//add values to a set.  The set retains only unique names.
names.add("James");
names.add("James");
names.add("Matthew");
names.add("Mark");
names.add("Matthew");
names.add("Mark");
names.add("Luke");
names.add("John");

//retrieve Set.
names;   

//Add more names as an ArrayList.
List<String> names = Arrays.asList("Jon","Garfield","Odie");

Set<String> uniqueNames = new TreetSet<String>(names);

• SortedSets are an upgrade of TreeSets so more methods can be performed on them. such as headSet(), tailset() and subset();

SortedSet<String> uniqueNames = new TreeSet<String>(names);

  set.headSet("J");
  //returns everything beginning before J
  set.tailSet("J");   
  //returns everything beginning after J
  set.subSet("Java", "Java" + Character.MAX_VALUE);
  //a searched list of everything beginning with J

HashSet - an implementation of a list with unique values only. TreeSet - an alphabetically sorted implementation of a list with unique values only.