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🏷 Functional Programming 5 patterns

Topic: Functional Programming

All Java patterns related to Functional Programming — java.evolved

Anonymous classes to lambdas and method references

Old button.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent event) { save(event); } });

Modern button.addActionListener(this::save);

hover to see modern →

JDK 8+ learn more →

Atomic map updates with compute and merge

Old List<String> values = groups.get(key); if (values == null) { values = new ArrayList<>(); groups.put(key, values); } values.add(value);

Modern groups.computeIfAbsent(key, ignored -> new ArrayList<>()) .add(value);

hover to see modern →

JDK 8+ learn more →

Collection bulk operations instead of mutation loops

Old for (Iterator<Order> it = orders.iterator(); it.hasNext();) { if (it.next().cancelled()) { it.remove(); } }

Modern orders.removeIf(Order::cancelled);

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JDK 8+ learn more →

Comparator factories and fluent ordering

Old people.sort(new Comparator<Person>() { @Override public int compare(Person a, Person b) { int byName = a.name().compareTo(b.name()); return byName != 0 ? byName : Integer.compare(a.age(), b.age()); } });

Modern people.sort(Comparator.comparing(Person::name) .thenComparingInt(Person::age));

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JDK 8+ learn more →

Predicate.not() for negation

Old List<String> nonEmpty = list.stream() .filter(s -> !s.isBlank()) .collect(Collectors.toList());

Modern List<String> nonEmpty = list.stream() .filter(Predicate.not(String::isBlank)) .collect(Collectors.toList());

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JDK 11+ learn more →