Sinhronizacija so pomos na Mutex

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class MutexLibrary {
    List<String> books = new ArrayList<>();
    int kapacitet; //kolku knigi sobira vo bibliotekata
    public static Lock lock = new ReentrantLock();


    public MutexLibrary(int kapacitet) {
        this.kapacitet = kapacitet;
    }

    //slucaj koga clenot treba da vrati kniga vo bibliotekatta

    public void returnBook(String book) throws InterruptedException {
        lock.lock();
        while (true) {
            if (books.size() < kapacitet) {
                books.add(book);
                lock.unlock();
                break;
            }
            lock.unlock();
        }
    }


    //slucaj kgoa clenot treba da zeme kniga od bibliotekata

    public String borrowBook() throws InterruptedException {
        String book = "";
        while (true) {
            lock.lock();
            if (books.size() > 0) {
                book = books.remove(0);
                lock.unlock();
                break;
            }
            lock.unlock();
        }
        return book;
    }
}