Language

Raw collections to generic types

Old List names = new ArrayList(); names.add("Duke"); String name = (String) names.get(0);

Modern List<String> names = new ArrayList(); names.add("Duke"); String name = names.get(0);

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JDK 5+ learn more →

Collections

Immutable list creation

Old List<String> list = Collections.unmodifiableList( new ArrayList<>( Arrays.asList("a", "b", "c") ) );

Modern List<String> list = List.of("a", "b", "c");

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JDK 9+ learn more →

Collections

Immutable map creation

Old Map<String, Integer> map = new HashMap<>(); map.put("a", 1); map.put("b", 2); map.put("c", 3); map = Collections.unmodifiableMap(map);

Modern Map<String, Integer> map = Map.of("a", 1, "b", 2, "c", 3);

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JDK 9+ learn more →

Collections

Immutable set creation

Old Set<String> set = Collections.unmodifiableSet( new HashSet<>( Arrays.asList("a", "b", "c") ) );

Modern Set<String> set = Set.of("a", "b", "c");

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JDK 9+ learn more →

Collections

Copying collections immutably

Old List<String> copy = Collections.unmodifiableList( new ArrayList<>(original) );

Modern List<String> copy = List.copyOf(original);

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JDK 10+ learn more →

Collections

Map.entry() factory

Old Map.Entry<String, Integer> e = new AbstractMap.SimpleEntry<>( "key", 42 );

Modern var e = Map.entry("key", 42);

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JDK 9+ learn more →

Collections

Sequenced collections

Old // Get last element Object last = list.get(list.size() - 1); // Get first Object first = list.get(0); // Reverse iteration: manual

Modern var last = list.getLast(); var first = list.getFirst(); var reversed = list.reversed();

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JDK 21+ learn more →

Collections

Typed stream toArray

Old List<String> list = getNames(); List<String> filtered = new ArrayList<>(); for (String n : list) { if (n.length() > 3) { filtered.add(n); } } String[] arr = filtered.toArray(new String[0]);

Modern String[] arr = getNames().stream() .filter(n -> n.length() > 3) .toArray(String[]::new);

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JDK 8+ learn more →

Collections

Reverse list iteration

Old for (ListIterator<String> it = list.listIterator(list.size()); it.hasPrevious(); ) { String element = it.previous(); System.out.println(element); }

Modern for (String element : list.reversed()) { IO.println(element); }

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JDK 21+ learn more →

Collections

Unmodifiable collectors

Old List<String> list = stream.collect( Collectors.collectingAndThen( Collectors.toList(), Collections::unmodifiableList ) );

Modern List<String> list = stream.toList();

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JDK 16+ learn more →

Collections

Legacy synchronized collections to modern alternatives

Old Hashtable<String, Session> sessions = new Hashtable<>(); sessions.put(id, session);

Modern ConcurrentMap<String, Session> sessions = new ConcurrentHashMap<>(); sessions.put(id, session);

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JDK 5+ learn more →

Collections

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);

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JDK 8+ learn more →

Collections

Stack to Deque and ArrayDeque

Old Stack<String> stack = new Stack<>(); stack.push("task"); String next = stack.pop();

Modern Deque<String> stack = new ArrayDeque<>(); stack.push("task"); String next = stack.pop();

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JDK 6+ learn more →

Collections

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 →

Collections

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 →

Streams

Stream.toList()

Old List<String> result = stream .filter(s -> s.length() > 3) .collect(Collectors.toList());

Modern List<String> result = stream .filter(s -> s.length() > 3) .toList();

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JDK 16+ learn more →