import java.util.Queue;
import java.util.LinkedList;
import java.util.Random;
 
class Main {
	public static void main(String[] args) {
		// Разделяемые потоками ресурсы - буфер и монитор
		final Queue<String> sharedBuffer = new LinkedList<>();
		final Object sharedMonitor = new Object();
 
		// Потоки, пока не запускаются
		final Thread adder = new Adder(sharedBuffer, sharedMonitor),
			printer = new Printer(sharedBuffer, sharedMonitor);
 
		// Если все написано верно, вне зависимости от порядка запуска потоки 
		// отрабатают без дедлоков
		if (new Random().nextBoolean()) {
			adder.start();
			printer.start();
		} else {
			printer.start();
			adder.start();
		}
	}
}
 
/* Producer */
class Adder extends Thread {
	private final Queue<String> buffer;
	private final Object monitor;
 
	public Adder(Queue<String> buffer, Object monitor) {
		this.buffer = buffer;
		this.monitor = monitor;
	}
 
	@Override
	public void run() {
		for (int i = 0; i < 2; i++) {
			// Захватываем монитор
			synchronized (monitor) {
				// Добавляем строки в буфер
				buffer.add("foo " + i);
				buffer.add("bar " + i);
				// Будим поток-потребитель
				monitor.notify();
				// И засыпаем пока он не обработает строки в буфере
				while (buffer.size() != 0) {
					try {
						monitor.wait();
					} catch (InterruptedException ex) {
						ex.printStackTrace();
					}
				}
			}
		}
	}
}
 
/* Consumer */
class Printer extends Thread {
	private final Queue<String> buffer;
	private final Object monitor;
 
	public Printer(Queue<String> buffer, Object monitor) {
		this.buffer = buffer;
		this.monitor = monitor;
	}
 
	@Override
	public void run() {
		for (int i = 0; i < 2; i++) {
			// Захватываем монитор
			synchronized (monitor) {
				// Спим пока поток-производитель не положит в буфер строки
				while (buffer.size() != 2) {
					try {
						monitor.wait();
					} catch (InterruptedException ex) {
						ex.printStackTrace();
					}
				}
				// Достаем строки из буфера и печатаем
				System.out.println(buffer.poll());
				System.out.println(buffer.poll());
				// Будим поток-производитель
				monitor.notify();
			}
		}
	}
}

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