Speaker: Venkat Subramaniam

See the table of contents for more posts

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Exercise 0 – warm up

• How many years have you been doing Java

Exercise 1 – Collection’s remove

• An ArrayList containing 1, 2, 3 becomes 1, 3 when call remove(1)
• If you change to Collection<Integer> numbers = new ArrayList<>, what happens.
• It is [2,3] because uses method on Collection, not on the ArrayList
• “Code always does what you type and not what you mean”

Exercise 2: type inference

• Exercise 1 but with var numbers = new ArrayList<>()
• now it is [1,3] because var uses type on right which is ArrayList
• Just because you like type inference doesn’t mean use it all the time. Determine when right thing to do

Exercise 3: Arrays.asList()

• Arrays.asList(1, 2, 3)
• Which of add/set are printed and what is in list?
• add throws exception, set works so it is [1,2, 2]
• Lesson: quit using asList. Use List.of instead

Exercise 4: forEach

• .forEach(name -> upper.add(name))
• worked until made one change
• side effects is the problem (change was probably making it parallel)
• forgot “it works on my machine”. better is “it failed on my machine”. Want it to fail on your machine instead of in prod
• The lambda is not pure. A pure function is idempotent. Returns same result for same input regardless of how many times it is called.
• A pure function does not emphasize anything outside it. It is ok to mutate; it’s like changing clothes. Just don’t do so in public; aka as a side effect
• A pure function does not depending on anything outside that may possibly change.

Exercise 5: stream

• int[] factor= new int[]1,2,3};
• stream = numbers.stream().map(n -> n * factor[0]);
• factor[0] = 0;
• stream.forEach(System.out::println)
• 000 because lazy evaluation

My take

This was cool. It wasn’t Venkat’s usual style. It was more interactive. He had a QR code to a Google form for each exercise so the audience could reply. That’s a great technique. If I ever have to present remotely about certifications, I’m going to copy it! It was interesting seeing the Google form results A lot of mixed results