The following table summarizes the principal classes in Java collections framework for quick reference:

• D: Duplicate elements is allowed?
• O: Elements are ordered?
• S: Elements are sorted?
• TS: The collection is thread-safe?

From this table we can conclude the following characteristics of the main collections in Java Collection Frameworks:

• •           All lists allow duplicate elements which are ordered by index.
  •           All sets and maps do not allow duplicate elements.
  •           All list elements are not sorted.
  •           Generally, sets and maps do not sort its elements, except TreeSet and TreeMap – which sort elements by natural order or by a comparator.
  •           Generally, elements within sets and maps are not ordered, except for:
    • •    LinkedHashSet and LinkedHashMap have elements ordered by insertion order.
      •       TreeSet and TreeMap have elements ordered by natural order or by a comparator.
  •           There are only two collections are thread-safe: Vectorand Hastable. The rest is not thread-safe.

Java Collections Tutorials:

• What is Java Collections Framework?
• Java List Tutorial
• Java Set Tutorial
• Java Map Tutorial
• Java Queue Tutorial
• Understanding Collections and Thread Safety in Java
• Understanding equals and hashCode in Java
• 18 Java Collections and Generics Best Practices
• Understanding Object Ordering in Java