public sealed class Vehicle permits Car, Truck, Bus {} final class Bus extends Vehicle { } non-sealed class Truck extends Account { } sealed class Car permits BlueCar, RedCar{ } public abstract sealed class User permits PremiumUser, AdvancedUser { public abstract String getUserData(); } non-sealed class PremiumUser extends User { @Override public String getUserData() {…
Read More Sealed Classes and Interfaces in Javaclass Test { public static void main(String[] args) { String name = null; System.out.println(name.toUpperCase()); } } Output: Exception in thread “main” java.lang.NullPointerException at com.example.Test.main (Test.java:9) Here, we got an error message that the NPE has occurred on line 9. Unfortunately, we can’t conclude which value exactly was null from the message. class Test { public static…
Read More Helpful NullPointerExceptions (NPE) in Javaclass Test { public static void main(String[] args) { Vehicle vehicle = new Car(); if (vehicle instanceof Car) { Car car = (Car) vehicle; car.openTrunk(); // other code … } else if (vehicle instanceof Truck) { Truck truck = (Truck) vehicle; truck.removeTrailer(); // other code … } } } class Test { public static void…
Read More Java Pattern Matching for instanceofclass User { private String name; private String username; private String membershipType; private String address; public User(String name, String username, String membershipType, String address) { this.name = name; this.username = username; this.membershipType = membershipType; this.address = address; } public String getName() { return name; } public void setName(String name) { this.name = name; } public…
Read More Java RecordsString multilineText= “”” Hi, this is one simple example of a multiline text”””; class Test { public static void main(String[] args) { String example = “{\”key1\”:\”value1\”,\”key2\”:” + “\”value2\”,\”key3\”:\”value3\”}”; System.out.println(example); } } Output: {“key1″:”value1″,”key2″:”value2″,”key3″:”value3”} Now, let’s use a Text Block: class Test { public static void main(String[] args) { String example = “”” { “key1”:…
Read More Java Text Blocksclass Test { public static void main(String[] args) { System.out.println(Runtime.getRuntime().availableProcessors()); } } IntStream.rangeClosed(1, 100000) .parallel() .sum();
Read More Parallel Streams – How does it work?private static void sumWithRegularStream() { for (int i = 0; i < 10; i++) { IntStream.rangeClosed(1, 100000).sum(); } } private static void sumWithParallelStream() { for (int i = 0; i < 10; i++) { IntStream.rangeClosed(1, 100000).parallel().sum(); } } class Test { public static void main(String[] args) { long regularStreamStartTime = System.currentTimeMillis(); sumWithRegularStream(); System.out.println(“Regular Stream execution…
Read More Parallel Streams Performance Testingclass Test { public static void main(String[] args) { System.out.println(“Normal Stream…”); IntStream integers = IntStream.rangeClosed(1, 10); integers.forEach(num -> System.out.print(num + ” “)); System.out.println(); System.out.println(“Parallel Stream…”); IntStream integers2 = IntStream.rangeClosed(1, 10); integers2.parallel().forEach(num -> System.out.print(num + ” “)); } } Output: Normal Stream… 1 2 3 4 5 6 7 8 9 10 Parallel Stream… 7 6…
Read More Introduction to Parallel Streams API in Javaclass Test { public static void main(String[] args) { Optional<String> stringOptional = Optional.ofNullable(“value1”); stringOptional.map(value -> value.concat(“234”)) .ifPresent(System.out::println); } } Output: value1234 2. Using the flatMap() method class Student { private String firstName; private String lastName; private int grade; private Optional<String> address; public Student(String firstName, String lastName, int grade) { this.firstName = firstName; this.lastName = lastName;…
Read More Optional – map() and flatMap() operationspublic Optional<T> filter(Predicale<T> predicate) class Test { public static void main(String[] args) { Optional<String> stringOptional = Optional.ofNullable(“alegru coding”); stringOptional.filter(str -> str.length() > 10) .map(String::toUpperCase) .ifPresent(System.out::println); } } Output: ALEGRU CODING class Test { public static void main(String[] args) { Optional<User> userOptional = Optional.ofNullable(new User(“John”, “john123”, “premium”, “5th Avenue”)); userOptional.filter(user -> user.getMembershipType().equals(“premium”)) .ifPresent(System.out::println); } } class…
Read More Optional – filter() operationIn this lesson, we will cover the three useful methods from the Optional class: public T orElse(T other) – It returns the value if present, otherwise returns the other. public T orElseGet(Supplier<? extends T> other) – It returns the value if present. Otherwise, invoke other and return the result of that invocation. public <X extends…
Read More Optional – orElse(), orElseGet() and orElseThrow() methodsWe have the isPresent() and ifPresent() methods to help us detect if Optional contains some value or not. Optional isPresent() method The isPresent() method returns true if there is a value present in the Optional, otherwise false.Using it, we can avoid getting an exception when trying to get the value from an empty Optional. So…
Read More Optional – ifPresent() and isPresent() methodsclass Test { public static void main(String[] args) { Optional optional = Optional.empty(); // creates an empty Optional if (optional.isEmpty()) { System.out.println(“It is an empty Optional.”); } else { System.out.println(“Optional is not empty.”); } } } Output: It is an empty Optional. 2. Optional.of(T value) method class Test { public static void main(String[] args) {…
Read More Introduction to Optional class in Javapublic static <T, K> Collector<T, ?, Map<K, List<T>>> groupingBy(Function<? super T, ? extends K> classifier) class Test { public static void main(String[] args) { List<String> cities = new ArrayList<>(Arrays.asList(“Paris”, “Bern”, “London”, “Tokyo”, “Boston”)); Map<Integer, List<String>> resultMap = cities.stream() .collect(Collectors.groupingBy(String::length)); System.out.println(resultMap); } } Output: {4=[Bern], 5=[Paris, Tokyo], 6=[London, Boston]} class Test { public static void main(String[]…
Read More Streams – groupingBy() operation