Java | Фишки и трюки

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();
            }
        }
    }
}

class Test {
   int a = 0b1101010110;
   public static void main(String[] args) {
       System.out.println("Hello world!");       
   }
}

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-actuator</artifactId>
</dependency>

management.endpoints.web.exposure.include=health,info,metrics
management.endpoint.health.show-details=always

public class Quest {
    public static void main(String[] args) {
        System.out.println(calc(10, 5));
    }

    private static int calc(int i, int j) {
        int result = i + j;
        return result;

        result = i - j;
        return result;
    }
}

public class Quest {
    public static void main(String[] args) {
        System.out.println(concat1() < concat2());
    }
    private static long concat1() {
        long start = System.nanoTime();
        String s = "";
        for (int i = 0; i < 1000; i++) {
            s += "-" + i;
        }
        return System.nanoTime() - start;
    }

    private static long concat2() {
        long start = System.nanoTime();
        StringBuilder s = new StringBuilder();
        for (int i = 0; i < 1000; i++) {
            s.append("-" + i);
        }
        return System.nanoTime() - start;
    }
}

Parent parent = new Child();
if (parent instanceof Child) {
    Child child = (Child) parent;
}

public final class Objects {
    private Objects() {
        throw new AssertionError("No java.util.Objects instances for you!");
    }
    ...
}

public static boolean equals(Object a, Object b) {
    return (a == b) || (a != null && a.equals(b));
}

public static String toString(Object o) {
    return String.valueOf(o);
}

public static String toString(Object o, String nullDefault) {
    return (o != null) ? o.toString() : nullDefault;
}

public static <T> T requireNonNull(T obj) {
    if (obj == null)
        throw new NullPointerException();
    return obj;
}

public static boolean isNull(Object obj) {
    return obj == null;
}

public static boolean nonNull(Object obj) {
    return obj != null;
}

public class Quest {
    public static void main(String[] args) {
        Short b = 50;
        inc(b);
        System.out.println(b);
    }
    private static void inc(Short num) {
        num++;
    }
}