collections.md

Collections

Collections don't accept primitive types.

Use wrapper classes.

• List
  • ArrayList
  • LinkedList
  • Vector
  • Stack
• Set
  • HashSet
  • TreeSet
  • LinkedHashSet
• Queue
  • PriorityQueue
  • ArrayDeque
• Map
  • HashMap
  • TreeMap
  • HashTable

Generics

Controlling inner objects types with implicit casting.

Generics examples:

// one inner type
ArrayList<Integer> list = new ArrayList<Integer>();

// two inner types
HashMap<Integer, String> map = new HashMap<Integer, String>();

// Generic as an inner type
ArrayList<ArrayList<String>> lists = new ArrayList<ArrayList<String>>();

public class MultiPart<T, E> extends AbstractPart<E> {
   // ...
}

public class Part<T extends SuperT> {
   // ...
}

ArrayList

Syntax sugar:

ArrayList<String> list = new ArrayList<String>();
list.add("Hello");
list.add("world");

ArrayList<String> list1 = new ArrayList<String>()
{{
   add("Hello");
   add("world");
}};

var list2 = new ArrayList<String>()
{{
   add("Hello");
   add("world");
}};