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Added priority queue design pattern (#888)

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* added priority queue design pattern

* Minor Refactored, fixed review comments
This commit is contained in:
Ranjeet 2019-08-31 23:40:35 +05:30 committed by Ilkka Seppälä
parent 11c0550559
commit 7f6067f19f
10 changed files with 616 additions and 7 deletions
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pom.xml
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE. THE SOFTWARE.
--><project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> -->
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion> <modelVersion>4.0.0</modelVersion>
<groupId>com.iluwatar</groupId> <groupId>com.iluwatar</groupId>
<artifactId>java-design-patterns</artifactId> <artifactId>java-design-patterns</artifactId>
@ -166,6 +168,7 @@
<module>collection-pipeline</module> <module>collection-pipeline</module>
<module>master-worker-pattern</module> <module>master-worker-pattern</module>
<module>spatial-partition</module> <module>spatial-partition</module>
<module>priority-queue</module>
<module>commander</module> <module>commander</module>
<module>typeobjectpattern</module> <module>typeobjectpattern</module>
</modules> </modules>

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priority-queue/README.md Normal file
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---
layout: pattern
title: Priority Queue Pattern
folder: priority-queue
permalink: /patterns/priority-queue/
categories: Behavioral
tags:
- Java
- Difficulty-Beginner
---
## Intent
Prioritize requests sent to services so that requests with a higher priority are received and processed more quickly than those of a lower priority. This pattern is useful in applications that offer different service level guarantees to individual clients.
## Explanation
Applications may delegate specific tasks to other services; for example, to perform background processing or to integrate with other applications or services. In the cloud, a message queue is typically used to delegate tasks to background processing. In many cases the order in which requests are received by a service is not important. However, in some cases it may be necessary to prioritize specific requests. These requests should be processed earlier than others of a lower priority that may have been sent previously by the application.
## Applicability
Use the Property pattern when
* The system must handle multiple tasks that might have different priorities.
* Different users or tenants should be served with different priority..
## Real world examples
* [ Priority Queue Pattern](https://docs.microsoft.com/en-us/previous-versions/msp-n-p/dn589794(v=pandp.10))
Microsoft Azure does not provide a queuing mechanism that natively support automatic prioritization of messages through sorting. However, it does provide Azure Service Bus topics and subscriptions, which support a queuing mechanism that provides message filtering, together with a wide range of flexible capabilities that make it ideal for use in almost all priority queue implementations.

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<?xml version="1.0" encoding="UTF-8"?>
<!--
The MIT License
Copyright (c) 2014 Ilkka Seppälä
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
-->
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<artifactId>priority-queue</artifactId>
<parent>
<groupId>com.iluwatar</groupId>
<artifactId>java-design-patterns</artifactId>
<version>1.21.0-SNAPSHOT</version>
</parent>
<dependencies>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-engine</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
</project>

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priority-queue/src/main/java/com/iluwatar/priority/queue/Application.java Normal file
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/**
* The MIT License
* Copyright (c) 2014 Ilkka Seppälä
* <p>
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.priority.queue;
/**
* Prioritize requests sent to services so that requests with a higher priority are received and
* processed more quickly than those of a lower priority.
* This pattern is useful in applications that offer different service level guarantees
* to individual clients.
* Example :Send multiple message with different priority to worker queue.
* Worker execute higher priority message first
* @see "https://docs.microsoft.com/en-us/previous-versions/msp-n-p/dn589794(v=pandp.10)"
*/
public class Application {
/**
* main entry
*/
public static void main(String[] args) throws Exception {
QueueManager queueManager = new QueueManager(100);
// push some message to queue
// Low Priority message
for (int i = 0; i < 100; i++) {
queueManager.publishMessage(new Message("Low Message Priority", 0));
}
// High Priority message
for (int i = 0; i < 100; i++) {
queueManager.publishMessage(new Message("High Message Priority", 1));
}
// run worker
Worker worker = new Worker(queueManager);
worker.run();
}
}

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priority-queue/src/main/java/com/iluwatar/priority/queue/Message.java Normal file
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/**
* The MIT License
* Copyright (c) 2014 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.priority.queue;
/**
* Message bean
*/
public class Message implements Comparable<Message> {
private final String message;
private final int priority; // define message priority in queue
public Message(String message, int priority) {
this.message = message;
this.priority = priority;
}
@Override
public int compareTo(Message o) {
return priority - o.priority;
}
@Override
public String toString() {
return "Message{"
+ "message='" + message + '\''
+ ", priority=" + priority
+ '}';
}
}

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priority-queue/src/main/java/com/iluwatar/priority/queue/PriorityMessageQueue.java Normal file
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/**
* The MIT License
* Copyright (c) 2014 Ilkka Seppälä
* <p>
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.priority.queue;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import static java.util.Arrays.copyOf;
/**
* Keep high Priority message on top using maxHeap.
*
* @param <T> : DataType to push in Queue
*/
public class PriorityMessageQueue<T extends Comparable> {
private static final Logger LOGGER = LoggerFactory.getLogger(PriorityMessageQueue.class);
private int size = 0;
private int capacity;
private T[] queue;
public PriorityMessageQueue(T[] queue) {
this.queue = queue;
this.capacity = queue.length;
}
/**
* Remove top message from queue
*/
public T remove() {
if (isEmpty()) {
return null;
}
T root = queue[0];
queue[0] = queue[size - 1];
size--;
maxHeapifyDown();
return root;
}
/**
* Add message to queue
*/
public void add(T t) {
ensureCapacity();
queue[size] = t;
size++;
maxHeapifyUp();
}
/**
* Check queue size
*/
public boolean isEmpty() {
return size == 0;
}
private void maxHeapifyDown() {
int index = 0;
while (hasLeftChild(index)) {
int smallerIndex = leftChildIndex(index);
if (hasRightChild(index) && right(index).compareTo(left(index)) > 0) {
smallerIndex = rightChildIndex(index);
}
if (queue[index].compareTo(queue[smallerIndex]) > 0) {
break;
} else {
swap(index, smallerIndex);
}
index = smallerIndex;
}
}
private void maxHeapifyUp() {
int index = size - 1;
while (hasParent(index) && parent(index).compareTo(queue[index]) < 0) {
swap(parentIndex(index), index);
index = parentIndex(index);
}
}
// index
private int parentIndex(int pos) {
return (pos - 1) / 2;
}
private int leftChildIndex(int parentPos) {
return 2 * parentPos + 1;
}
private int rightChildIndex(int parentPos) {
return 2 * parentPos + 2;
}
// value
private T parent(int childIndex) {
return queue[parentIndex(childIndex)];
}
private T left(int parentIndex) {
return queue[leftChildIndex(parentIndex)];
}
private T right(int parentIndex) {
return queue[rightChildIndex(parentIndex)];
}
// check
private boolean hasLeftChild(int index) {
return leftChildIndex(index) < size;
}
private boolean hasRightChild(int index) {
return rightChildIndex(index) < size;
}
private boolean hasParent(int index) {
return parentIndex(index) >= 0;
}
private void swap(int fpos, int tpos) {
T tmp = queue[fpos];
queue[fpos] = queue[tpos];
queue[tpos] = tmp;
}
private void ensureCapacity() {
if (size == capacity) {
capacity = capacity * 2;
queue = copyOf(queue, capacity);
}
}
/**
* For debug .. print current state of queue
*/
public void print() {
for (int i = 0; i <= size / 2; i++) {
LOGGER.info(" PARENT : " + queue[i] + " LEFT CHILD : "
+ left(i) + " RIGHT CHILD :" + right(i));
}
}
}

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priority-queue/src/main/java/com/iluwatar/priority/queue/QueueManager.java Normal file
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/**
* The MIT License
* Copyright (c) 2014 Ilkka Seppälä
* <p>
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.priority.queue;
/**
* Manage priority queue
*/
public class QueueManager {
/*
Priority message
*/
private final PriorityMessageQueue<Message> messagePriorityMessageQueue;
public QueueManager(int initialCapacity) {
messagePriorityMessageQueue = new PriorityMessageQueue<Message>(new Message[initialCapacity]);
}
/**
* Publish message to queue
*/
public void publishMessage(Message message) {
messagePriorityMessageQueue.add(message);
}
/**
* recive message from queue
*/
public Message receiveMessage() {
if (messagePriorityMessageQueue.isEmpty()) {
return null;
}
return messagePriorityMessageQueue.remove();
}
}

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priority-queue/src/main/java/com/iluwatar/priority/queue/Worker.java Normal file
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/**
* The MIT License
* Copyright (c) 2014 Ilkka Seppälä
* <p>
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* <p>
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* <p>
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.priority.queue;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Message Worker
*/
public class Worker {
private static final Logger LOGGER = LoggerFactory.getLogger(Worker.class);
private final QueueManager queueManager;
public Worker(QueueManager queueManager) {
this.queueManager = queueManager;
}
/**
* Keep checking queue for message
*/
public void run() throws Exception {
while (true) {
Message message = queueManager.receiveMessage();
if (message == null) {
LOGGER.info("No Message ... waiting");
Thread.sleep(200);
} else {
processMessage(message);
}
}
}
/**
* Process message
*/
private void processMessage(Message message) {
LOGGER.info(message.toString());
}
}

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priority-queue/src/test/java/com/iluwatar/priority/queue/PriorityMessageQueueTest.java Normal file
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/**
* The MIT License
* Copyright (c) 2014 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.priority.queue;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertTrue;
/**
* Test case for order of messages
*/
public class PriorityMessageQueueTest {
@Test
public void remove() {
PriorityMessageQueue<String> stringPriorityMessageQueue = new PriorityMessageQueue<>(new String[2]);
String pushMessage = "test";
stringPriorityMessageQueue.add(pushMessage);
assertEquals(stringPriorityMessageQueue.remove(), pushMessage);
}
@Test
public void add() {
PriorityMessageQueue<Integer> stringPriorityMessageQueue = new PriorityMessageQueue<>(new Integer[2]);
stringPriorityMessageQueue.add(1);
stringPriorityMessageQueue.add(5);
stringPriorityMessageQueue.add(10);
stringPriorityMessageQueue.add(3);
assertTrue(stringPriorityMessageQueue.remove() == 10);
}
@Test
public void isEmpty() {
PriorityMessageQueue<Integer> stringPriorityMessageQueue = new PriorityMessageQueue<>(new Integer[2]);
assertTrue(stringPriorityMessageQueue.isEmpty());
stringPriorityMessageQueue.add(1);
stringPriorityMessageQueue.remove();
assertTrue(stringPriorityMessageQueue.isEmpty());
}
@Test
public void testEnsureSize() {
PriorityMessageQueue<Integer> stringPriorityMessageQueue = new PriorityMessageQueue<>(new Integer[2]);
assertTrue(stringPriorityMessageQueue.isEmpty());
stringPriorityMessageQueue.add(1);
stringPriorityMessageQueue.add(2);
stringPriorityMessageQueue.add(2);
stringPriorityMessageQueue.add(3);
assertTrue(stringPriorityMessageQueue.remove() == 3);
}
}

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priority-queue/src/test/java/com/iluwatar/priority/queue/QueueManagerTest.java Normal file
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/**
* The MIT License
* Copyright (c) 2014 Ilkka Seppälä
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package com.iluwatar.priority.queue;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertEquals;
/**
* Check queue manager
*/
public class QueueManagerTest {
@Test
public void publishMessage() {
QueueManager queueManager = new QueueManager(2);
Message testMessage = new Message("Test Message", 1);
queueManager.publishMessage(testMessage);
Message recivedMessage = queueManager.receiveMessage();
assertEquals(testMessage, recivedMessage);
}
@Test
public void receiveMessage() {
QueueManager queueManager = new QueueManager(2);
Message testMessage1 = new Message("Test Message 1", 1);
queueManager.publishMessage(testMessage1);
Message testMessage2 = new Message("Test Message 2", 2);
queueManager.publishMessage(testMessage2);
Message recivedMessage = queueManager.receiveMessage();
assertEquals(testMessage2, recivedMessage);
}
}