Java | Фишки и трюки

unmodifiableCollection
unmodifiableSequencedCollection
unmodifiableSet
unmodifiableSequencedSet
unmodifiableSortedSet
unmodifiableNavigableSet
unmodifiableList
unmodifiableMap
unmodifiableSequencedMap
unmodifiableSortedMap
unmodifiableNavigableMap

List<String> list = new ArrayList<>();
list.add("A");
list.add("B");
list.add("C");
List<String> unmodifiableList = Collections.unmodifiableList(list);
// Попытка изменить unmodifiableList приведет к UnsupportedOperationException
// unmodifiableList.remove("B");

import java.util.List;
import java.util.TreeSet;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Quest {
    public static void main(String[] args) {
        List<String> list = Stream.of("Pizza", "Sushi", "Pasta", "Sushi", "Pizza")
                .sequential()
                .filter(new TreeSet<>()::add)
                .collect(Collectors.toList());
        System.out.println(list);
    }
}

class Task implements Comparable<Task> {
    String name;
    Integer priority;

    public Task(String name, Integer priority) {
        this.name = name;
        this.priority = priority;
    }

    @Override
    public int compareTo(@NotNull Task o) {
        return priority - o.priority;
    }
}

public class Test {
    public static void main(String[] args) {
        PriorityQueue<Task> pq = new PriorityQueue<>();

        pq.add(new Task("Task1", 1));
        pq.add(new Task("Task5", 5));
        pq.add(new Task("Task2", 2));
        pq.add(new Task("Task4", 4));
        pq.add(new Task("Task3", 3));

        while (!pq.isEmpty()) {
            System.out.println(pq.poll().name);
            // Выведет: Task1, Task2, Task3, Task4, Task5
        }
    }
}

class Task implements Comparable<Task> {
    String name;
    Integer priority;

    public Task(String name, Integer priority) {
        this.name = name;
        this.priority = priority;
    }

    @Override
    public int compareTo(@NotNull Task o) {
        return priority - o.priority;
    }
}

public class Test {
    public static void main(String[] args) {
        PriorityQueue<Task> pq = new PriorityQueue<>();

        pq.add(new Task("Task1", 1));
        pq.add(new Task("Task5", 5));
        pq.add(new Task("Task2", 2));
        pq.add(new Task("Task4", 4));
        pq.add(new Task("Task3", 3));

        while (!pq.isEmpty()) {
            System.out.println(pq.poll().name);
            // Выведет: Task1, Task2, Task3, Task4, Task5
        }
    }
}

String name = "Melissa";
System.out.println("Hello, \{name}!");
// Hello, Melissa!

public class Quest {
    public final int value = 4;
    public void doIt() {
        int value = 6;
        Runnable r = new Runnable() {
            public final int value = 8;
            public void run() {
                int value = 10;
                System.out.println(this.value);
            }
        };
        r.run();
    }
    public static void main(String[] args) {
        new Quest().doIt();
    }
}

import java.util.concurrent.Semaphore;

public class SemaphoreExample {
    private static final int MAX_CONCURRENT_THREADS = 3;
    private static final Semaphore semaphore = new Semaphore(MAX_CONCURRENT_THREADS);

    public static void main(String[] args) {
        for (int i = 0; i < 10; i++) {
            new Thread(new Worker(i)).start();
        }
    }

    static class Worker implements Runnable {
        private final int id;

        Worker(int id) {
            this.id = id;
        }

        @Override
        public void run() {
            try {
                System.out.println("Thread " + id + " is waiting for a permit.");
                semaphore.acquire();
                System.out.println("Thread " + id + " acquired a permit.");

                // Simulate some work with a sleep
                Thread.sleep(2000);

                System.out.println("Thread " + id + " releasing a permit.");
                semaphore.release();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}