example of queue

queue.java

package collections;

import java.io.IOException;
import java.util.Random;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.PriorityBlockingQueue;

class Program { 

    public static void main(String[] args) throws InterruptedException, IOException {

        Random rnd = new Random();
        Printer testprinter = new Printer("HP LaserJet 9050DN");
        int numberOfClients = 5;
        Client[] clients = new Client[numberOfClients];
        {
            for (int i = 0; i < numberOfClients; i++) {
                String name = "User-";
                for (int j = 0; j < 3; j++) {
                    name = name.concat(Integer.toString(rnd.nextInt(9)));
                }
                clients[i] = new Client(name, testprinter);
                System.out.println(clients[i].getName() + " start working.");
            }
            System.out.println();
        }

        PrintQueue printQueue = new PrintQueue(testprinter.priorityQueue);
        Thread print = new Thread(printQueue, "Print thread");
        print.start();

        while (true) {
            Thread.sleep((rnd.nextInt(3) + 3) * 1000);
            clients[rnd.nextInt(numberOfClients)].printNewDocument();

        }
    }
}

class PrintQueue implements Runnable {

    BlockingQueue<Document> queue;

    PrintQueue(BlockingQueue<Document> queue) {
        this.queue = queue;
    }

    public void run() {
        Random rnd = new Random();
        while (true) {
            if (queue.size() > 0) {
                Document doc = queue.poll();

                System.out.println("Document \"" + doc.getName() + "\" start printing.");
                try {
                    Thread.sleep(doc.getPages() * 3000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("Document \"" + doc.getName() + "\" finish printing.\n");
            } else {
                try {
                    Thread.sleep((rnd.nextInt(3) + 3) * 1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

class Printer {

    String printerName;
    BlockingQueue<Document> priorityQueue = new PriorityBlockingQueue<Document>();

    Printer(String name) {
        printerName = name;
        System.out.println("Printer " + printerName + " is ON.");
    }

    public void showQueue() {
        for (Document doc : priorityQueue) {
            System.out.println(doc + " by " + doc.client.getName());
        }
        System.out.println("--------------");
    }
}

class Document implements Comparable<Document> {

    private String documentName;
    private int pages;
    Client client;
    Random rnd = new Random();

    public Document(Client client) {
        this.client = client;
        documentName = randomName();
        pages = rnd.nextInt(3);
    }

    private String randomName() {
        char[] ch = new char[10];

        ch[0] = (char) (rnd.nextInt(26) + 64);

        for (int i = 1; i < 6; i++) {
            ch[i] = (char) (rnd.nextInt(26) + 97);
        }

        ch[6] = '-';

        for (int i = 7; i < 10; i++) {
            ch[i] = (char) (rnd.nextInt(9) + 48);
        }

        return new String(ch);
    }

    String getName() {
        return documentName;
    }

    int getPages() {
        return pages;
    }

    public String toString() {
        return documentName;
    }

    public int compareTo(Document doc) {
        int myPriority = Integer.parseInt(this.client.getName().substring(5));
        int hisPriority = Integer.parseInt(doc.client.getName().substring(5));
        return myPriority - hisPriority;
    }
}

class Client {

    private String clientName;
    Printer myPrinter;

    public Client(String name, Printer printer) {
        clientName = name;
        myPrinter = printer;
    }

    String getName() {
        return clientName;
    }

    public void printNewDocument() throws InterruptedException {
        Document doc = new Document(this);
        myPrinter.priorityQueue.add(doc);
        System.out.println("New document \"" + doc.getName() + "\" was sent to printer queue by " + clientName + ".");
    }
}