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Data Structures in Java

A thorough look at the collection classes in java.util.** in Java.

Heinz Kabutz

Java programmers typically use only very few collection classes for all of their work. Often they chose inappropriate ones. In this course, we will look at what each collection costs and when you should use which one. Some of the questions will we answer include: Which is the best Collection to use in Java? When do you need to employ ConcurrentSkipListSet? What is the computational time complexity of WeakHashMap?

What you'll learn-and how you can apply it

  • Java has an overwhelming number of interfaces and classes in the java.util.** packages. In this course you will learn what they are and when to use which. Is ArrayList better than LinkedList? What is the difference in space complexity between the two classes?
  • Choosing the correct collection can make our code more succinct. For example, the new List.of() syntax in Java 9 is better at creating immutable lists.
  • By looking at hashing closely, we can learn how to write hashing functions that produce a 3x performance improvement for HashMap and ConcurrentHashMap.
  • We learn when to use which concurrent classes and which to avoid.

This training course is for you because...

  • Junior and intermediate Java programmers wanting to understand collections better.
  • Advanced programmers who want to acquire additional skills.


  • Attendees should be familiar with basic Java code, but a CS degree is not assumed
  • Should know at least Java 6. We are covering all relevant collection classes up until Java 11. Knowledge of streams and lambdas not necessary.

Recommended Follow-up

Sign up to The Java Specialists’ Newsletter for lots of tips on the latest Java developments: https://www.javaspecialists.eu/archive

About your instructor

  • Heinz Kabutz is the author of “The Java Specialists’ Newsletter”, a publication enjoyed by tens of thousands of Java experts in over 145 countries. His book “Dynamic Proxies (in German)” was #1 Bestseller on Amazon.de in Fachbücher für Informatik for about five minutes until Amazon fixed their algorithm. Thanks to a supportive mother, he has now sold 5 copies.

    Heinz’s Java Specialists’ newsletter is filled with amusing anecdotes of life on the Island of Crete. He is a popular speaker at all the best Java conferences around the world, and also at some of the worst. He teaches Java courses in classrooms around the world, where his prime objective is to make absolutely sure that none of his students fall asleep. He is not always successful.


The timeframes are only estimates and may vary according to how the class is progressing

Section 1 - Introduction to Collections in Java (10 minutes)

  • Computational Time and Space Complexity
  • Arrays
  • Section 1 Quiz (5 minutes)

Section 2 – Lists (30 minutes)

  • Lists
  • ArrayList
  • Iteration
  • CopyOnWriteArrayList
  • LinkedList
  • Section 2 Quiz (5 minutes)

Section 3 – Sorting (25 minutes)

  • Sorting lists
  • Section 3 Quiz (5 minutes)

Section 4 – Sets (15 minutes)

  • Sets
  • TreeSet
  • ConcurrentSkipListSet
  • CopyOnWriteArraySet
  • Section 4 Quiz (5 minutes)

Section 5 – Hashing (15 minutes)

  • Hashing
  • HashSet
  • ConcurrentHashMap.newKeySet()
  • Section 5 Quiz (5 minutes)

Section 6 – Maps (45 minutes)

  • Maps
  • HashMap
  • ConcurrentHashMap
  • TreeMap
  • ConcurrentSkipListMap
  • LinkedHashMap and LinkedHashSet
  • Highly Specialized Collections: EnumSet, EnumMap, IdentityHashMap, Properties, WeakHashMap
  • Section 6 Quiz (5 minutes)

Section 7 - Queues and Deques (25 minutes)

  • Queues and Deques
  • ConcurrentLinkedQueue and ConcurrentLinkedDeque
  • ArrayDeque
  • BlockingQueues
  • LinkedBlockingQueue and LinkedBlockingDeque
  • ArrayBlockingQueue
  • Highly specialized queues: DelayQueue, SynchronousQueue, LinkedTransferQueue
  • PriorityQueue and PriorityBlockingQueue
  • Section 7 Quiz (5 minutes)

Section 8 - Collection Facades (15 minutes)

  • java.util.Collections
  • java.util.Arrays
  • Section 8 Quiz (5 minutes)

Section 9 – Wrap-up (15 minutes)

  • Further questions