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![Simone Bordet Mario Fusco Example #5, v2 Files.lines(Paths.get(filename)) .reduce(new LinkedList<String[]>(), (list, line) -> { if (!list.isEmpty()) list.getLast()[1] = line; list.offer(new String[]{line, null}); return list; }, (l1, l2) -> { l1.getLast()[1] = l2.getFirst()[0]; l1.addAll(l2); return l1; }).stream() .filter(ss -> ss[1] != null && ss[1].startsWith("ERROR")) .collect(Collectors.toList());](https://image.slidesharecdn.com/oopandfpv4-150329111521-conversion-gate01/75/OOP-and-FP-Become-a-Better-Programmer-27-2048.jpg)
![Simone Bordet Mario Fusco Example #8, v1 interface Shape2D { Shape2D move(int deltax, int deltay) } class Circle implements Shape { private final Point center; private final int radius; Circle move(int deltax, int deltay) { // translate the center } } class Polygon implements Shape { private final Point[] points; Polygon move(int deltax, int deltay) { // Translate each point. } }](https://image.slidesharecdn.com/oopandfpv4-150329111521-conversion-gate01/75/OOP-and-FP-Become-a-Better-Programmer-39-2048.jpg)
![Simone Bordet Mario Fusco Example #8, v2 defn move [shape, deltax, deltay] ( // Must crack open shape, then // figure out what kind of shape is // and then translate only the points ) OOP used correctly provides encapsulation FP must rely on OOP features to provide the same Data types are not enough Pattern matching is not enough Really need dynamic polimorphism](https://image.slidesharecdn.com/oopandfpv4-150329111521-conversion-gate01/75/OOP-and-FP-Become-a-Better-Programmer-41-2048.jpg)
Uploaded byMario Fusco
OOP and FP - Become a Better Programmer
This document presents a discussion on Object-Oriented Programming (OOP) and Functional Programming (FP) as two paradigms in programming, specifically focusing on their definitions in Java. It illustrates how each style offers distinct advantages for different programming scenarios, providing a variety of examples comparing OOP and FP approaches. The authors emphasize the importance of understanding both paradigms for becoming a better programmer and suggest guidelines for when to apply each approach.
OOP and FP - Become a Better Programmer
- 1. Simone Bordet Mario Fusco OOPand FP Become a Better Programmer
- 2. Our definition Of OOPand FP
- 3. Simone Bordet Mario Fusco OurDefinition of OOP In this presentation “OOP” will mean: Idiomatic Java 7 programming style: Use of mutable variables and state Use of classes and void methods Use of external iteration (for loops) Use of threads
- 4. Simone Bordet Mario Fusco Ourdefinition of FP In this presentation “FP” will mean: Java 8 programming style, with: Immutable variables and state Use classes, but avoid void methods Internal iteration via Stream CompletableFuture, not Thread
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- 6. Simone Bordet Mario Fusco Goals This session is about OOP and FP NOT about OOP versus FP We want to show that in order to be a better programmer, you have to know both In some cases it's better to apply one paradigm In other cases it's better to apply the other We will hint at some guideline that helps deciding
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- 8. Simone Bordet Mario Fusco Example#1, v1 public String sum(List<Student> students) { StringBuilder sb = new StringBuilder(); for (Student s : students) sb.append(s.getName()).append(“, “); return sb.toString(); } OOP style External iteration Mutable variables
- 9. Simone Bordet Mario Fusco Example#1, v2 public String sum(List<Student> students) { StringBuilder sb = new StringBuilder(); students.stream() .forEach(s -> sb.append(s.getName()).append(“, “)); return sb.toString(); } BAD style Use of mutable accumulator
- 10. Simone Bordet Mario Fusco Example#1, v3 public String sum(List<Student> students) { String names = students.stream() .map(s -> s.getName() + “, “) .reduce(“”, (a, b) -> a + b); return names; } FP style Internal iteration Mapping input to output No mutable variables
- 11. Example #2 “what doyou do ?”
- 12. Simone Bordet Mario Fusco Example#2, v1 What does this code do ? List<Student> students = ...; int min = 0; for (Student s : students) { if (s.getGradYear() != 2014) continue; int score = s.getGradScore(); if (score > min) min = score; }
- 13. Simone Bordet Mario Fusco Example#2, v2 Calculates the max, not the min ! And only for 2014 students ! List<Student> students = ...; students.stream() .filter(s -> s.getGradYear() == 2014) .mapToInt(Student::getScore) .max(); Somehow clearer to read Less possibility of mistakes max() is a method, not a variable name
- 14. Simone Bordet Mario Fusco Example#2, v3 But how do you get 2 results iterating once ? List<Student> students = ...; int min = Integer.MAX_VALUE, max = 0; for (Student s : students) { int score = s.getGradScore(); min = Math.min(min, score); max = Math.max(max, score); } Easy and readable
- 15. Simone Bordet Mario Fusco Example#2, v4 FP version: Pair<Integer, Integer> result = students.stream() .map(s -> new Pair<>(s.getScore(), s.getScore())) .reduce(new Pair<>(Integer.MAX_VALUE, 0), (acc,elem)-> { new Pair<>(Math.min(acc._1, elem._1), Math.max(acc._2, elem._2)) }); What !?!
- 16. Simone Bordet Mario Fusco Example#2, v5 How about parallelizing this ? Pair<Integer, Integer> result = students.stream().parallel() .map(s -> new Pair<>(s.getScore(), s.getScore())) .reduce(new Pair<>(Integer.MAX_VALUE, 0), (acc,elem)-> { new Pair<>(Math.min(acc._1, elem._1), Math.max(acc._2, elem._2)) }); Neat, but .parallel() can only be used under very strict conditions.
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- 18. Simone Bordet Mario Fusco Example#3, v1 Group students by their graduation year Map<Integer, List<Student>> studentByGradYear = new HashMap<>(); for (Student student : students) { int year = student.getGradYear(); List<Student> list = studentByGradYear.get(year); if (list == null) { list = new ArrayList<>(); studentByGradYear.put(year, list); } list.add(student); }
- 19. Simone Bordet Mario Fusco Example#3, v2 Map<Integer, List<Student>> studentByGradYear = students.stream() .collect(groupingBy(student::getGradYear));
- 20. Example #4 “separation ofconcerns”
- 21. Simone Bordet Mario Fusco Example#4, v1 Read first 40 error lines from a log file List<String> errorLines = new ArrayList<>(); int errorCount = 0; BufferedReader file = new BufferedReader(...); String line = file.readLine(); while (errorCount < 40 && line != null) { if (line.startsWith("ERROR")) { errorLines.add(line); errorCount++; } line = file.readLine(); }
- 22. Simone Bordet Mario Fusco Example#4, v2 List<String> errors = Files.lines(Paths.get(fileName)) .filter(l -> l.startsWith("ERROR")) .limit(40) .collect(toList());
- 23. Simone Bordet Mario Fusco Example#4 List<String> errorLines = new ArrayList<>(); int errorCount = 0; BufferedReader file = new BufferedReader(new FileReader(filename)); String line = file.readLine(); while (errorCount < 40 && line != null) { if (line.startsWith("ERROR")) { errorLines.add(line); errorCount++; } line = file.readLine(); } return errorLines; return Files.lines(Paths.get(fileName)) .filter(l -> l.startsWith("ERROR") .limit(40) .collect(toList());
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- 25. Simone Bordet Mario Fusco Example#5, v1 Find lines starting with “ERROR” and previous line List<String> errorLines = new ArrayList<>(); String previous = null; String current = reader.readLine(); while (current != null) { if (current.startsWith("ERROR")) { if (previous != null) errorLines.add(previous); errorLines.add(current); } previous = current; current = reader.readLine(); }
- 26. Simone Bordet Mario Fusco Example#5, v2 Not easy – immutability is now an obstacle Must read the whole file in memory This does not work: Stream.generate(() -> reader.readLine()) readLine() throws and can't be used in lambdas
- 27. Simone Bordet Mario Fusco Example#5, v2 Files.lines(Paths.get(filename)) .reduce(new LinkedList<String[]>(), (list, line) -> { if (!list.isEmpty()) list.getLast()[1] = line; list.offer(new String[]{line, null}); return list; }, (l1, l2) -> { l1.getLast()[1] = l2.getFirst()[0]; l1.addAll(l2); return l1; }).stream() .filter(ss -> ss[1] != null && ss[1].startsWith("ERROR")) .collect(Collectors.toList());
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- 29. Simone Bordet Mario Fusco Example#6, v1 Find a term, in parallel, on many search engines, then execute an action final List<SearchEngineResult> result = new CopyOnWriteArrayList<>(); final AtomicInteger count = new AtomicInteger(engines.size()); for (Engine e : engines) { http.newRequest(e.url("codemotion")).send(r -> { String c = r.getResponse().getContentAsString(); result.add(e.parse(c)); boolean finished = count.decrementAndGet() == 0; if (finished) lastAction.perform(result); }); }
- 30. Simone Bordet Mario Fusco Example#6, v1 Code smells Mutable concurrent accumulators: result and count Running the last action within the response callback What if http.newRequest() returns a CompletableFuture ? Then I would be able to compose those futures ! Let's try to write it !
- 31. Simone Bordet Mario Fusco Example#6, v2 CompletableFuture<List<SearchEngineResult>> result = CompletableFuture.completed(new CopyOnWriteArrayList<>()); for (Engine e : engines) { CompletableFuture<Response> request = http.sendRequest(e.url("codemotion")); result = result.thenCombine(request, (list, response) -> { String c = response.getContentAsString(); list.add(e.parse(c)); return list; }); } result.thenAccept(list -> lastAction.perform(list));
- 32. Simone Bordet Mario Fusco Example#6, v3 List<CompletableFuture<SearchEngineResult>> results = engines.stream() .map(e -> new Pair<>(e, http.newRequest(e.url("codemotion")))) .map(p -> p._2.thenCombine(response -> p._1.parse(response.getContentAsString()))) .collect(toList()); CompletableFuture.supplyAsync(() -> results.stream() .map(future -> future.join()) .collect(toList())) .thenApply(list -> lastAction.perform(list));
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- 34. Simone Bordet Mario Fusco Example#7, v1 class Cat { private Bird prey; private boolean full; void chase(Bird bird) { prey = bird; } void eat() { prey = null; full = true; } boolean isFull() { return full; } } class Bird { }
- 35. Simone Bordet Mario Fusco Example#7, v1 It is not evident how to use it: new Cat().eat() ??? The use case is instead: Cat useCase(Cat cat, Bird bird) { cat.chase(bird); cat.eat(); assert cat.isFull(); return cat; }
- 36. Simone Bordet Mario Fusco Example#7, v2 How about we use types to indicate state ? class Cat { CatWithPrey chase(Bird bird) { return new CatWithPrey(bird); } } class CatWithPrey { private final Bird prey; public CatWithPrey(Bird bird) { prey = bird; } FullCat eat() { return new FullCat(); } } class FullCat { }
- 37. Simone Bordet Mario Fusco Example#7, v2 Now it is evident how to use it: FullCat useCase(Cat cat, Bird bird) { return cat.chase(bird).eat(); } BiFunction<Cat, Bird, CatWithPrey> chase = Cat::chase; BiFunction<Cat, Bird, FullCat> useCase = chase.andThen(CatWithPrey::eat); More classes, but clearer semantic
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- 39. Simone Bordet Mario Fusco Example#8, v1 interface Shape2D { Shape2D move(int deltax, int deltay) } class Circle implements Shape { private final Point center; private final int radius; Circle move(int deltax, int deltay) { // translate the center } } class Polygon implements Shape { private final Point[] points; Polygon move(int deltax, int deltay) { // Translate each point. } }
- 40. Simone Bordet Mario Fusco Example#8, v1 for (Shape shape : shapes) shape.move(1, 2); How do you do this using an FP language ? What is needed is dynamic polymorphism Some FP language does not have it Other FP languages mix-in OOP features
- 41. Simone Bordet Mario Fusco Example#8, v2 defn move [shape, deltax, deltay] ( // Must crack open shape, then // figure out what kind of shape is // and then translate only the points ) OOP used correctly provides encapsulation FP must rely on OOP features to provide the same Data types are not enough Pattern matching is not enough Really need dynamic polimorphism
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- 43. Simone Bordet Mario Fusco Conclusions If you come from an OOP background Study FP If you come from an FP background Study OOP Poly-paradigm programming is more generic, powerful and effective than polyglot programming.
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