find and calculate address in an array for given index

I Was confused for how we get the address and address calculation done in an array when we get element from array for passing an index.

So, any data structure used to achieve this mechanism? is there any mapping in memory or hashing or indexing like used in DB? 

It is simple, just like mathematical formula.

Consider one dim array ARR of N integer(2 byte memory for each element) stored in memory.

Now, to find address of ARR[i]:

Adddress(ARR[i]) = Base Address + No. Of bytes for each element * (Find index - Lower bound of ARR)

Here, 

Base Address = starting address of an array in memory
No. Of bytes for each element  = for integer, it is 2 bytes
Find index = which element you are searching in an array
Lower bound of ARR = lower bound  index of array

For Ex. consider integer array int[] ARR = new int[4];

Address	Value	Element
100	11	1st
102	12	2nd
104	13	3rd
106	14	4th

As per above table, 

Addresss(ARR[2]) = 100 + 2* (2-0) = 100+4=104

Happy Learning!!!

4 things for to get max output from programming

4 things for to get max output from programming

1. Study and try to predict the behavior of the program
2. try to implement the behavior 
3. fix it if assuming it is broken
4. then and then look for expert solution

HashMap with Null Key and Null Value

HashMap does not call hashcode when null is passed as key and null Key is handled as special case.

Put Method

HashMap puts null key in bucket 0 and maps null as key to passed value. it does it by linked list data structure it uses internally.
Linked list data structure used by HashMap (a static class in HashMap.java)

static class Entry<K,V> implements Map.Entry<K,V> {
        final K key;
        V value;
        Entry<K,V> next;
        final int hash;
}

In Entry class the K is set to null and value mapped to value passed in put method.

Get Method

While in Hashmap get method the checks if key is passed as null. Search Value for null key in bucket 0.
Hence there can only be one null key in one hashmap object.

When you put NULL to HashMap there is special check if you are trying to put NULL as key (called putForNullKey()). It is special case and works not like you are trying to put some object which is not null, and as you may see it even doesn't go to hash calculation.

public V put(K key, V value) {
    if (table == EMPTY_TABLE) {
        inflateTable(threshold);
    }
    if (key == null)
        return putForNullKey(value);
    int hash = hash(key);
    int i = indexFor(hash, table.length);
    for (Entry<K,V> e = table[i]; e != null; e = e.next) {
        Object k;
        if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
            V oldValue = e.value;
            e.value = value;
            e.recordAccess(this);
            return oldValue;
        }
    }

    modCount++;
    addEntry(hash, key, value, i);
    return null;
}

private V putForNullKey(V value) {
    for (Entry<K,V> e = table[0]; e != null; e = e.next) {
        if (e.key == null) {
            V oldValue = e.value;
            e.value = value;
            e.recordAccess(this);
            return oldValue;
        }
    }
    modCount++;
    addEntry(0, null, value, 0);
    return null;
}

Docker Install error: Err:1 http://in.archive.ubuntu.com/ubuntu zesty/universe amd64 cgroupfs-mount all 1.3

I am using Ubuntu. while installing docker, I was getting below error, then I followed below steps to overcome the same.

 Err:1 http://in.archive.ubuntu.com/ubuntu zesty/universe amd64 cgroupfs-mount all 1.3


Open Terminal & run:

sudo gedit /etc/apt/sources.list
Replace url in.archive.ubuntu.com and security.ubuntu.com with old-releases.ubuntu.com

save and close it.

Now run sudo apt-get update and after then install any packages you want to install.

Then, I ran Docker install command,
sachin@sachin-E470:~$ sudo apt-get install docker-ce

sachin@sachin-E470:~$ docker --version

Docker version 17.12.0-ce, build c97c6d6

and its worked!!

SpringBoot RabbitMQ Integration

SpringBoot RabbitMQ Integration

Spring Integration enables lightweight messaging within Spring-based applications and supports integration with
external systems via declarative adapters. Those adapters provide a higher-level of abstraction over Spring's support
for remoting, messaging, and scheduling. Spring Integration's primary goal is to provide a simple model for building
enterprise integration solutions while maintaining the separation of concerns that is essential for producing
maintainable, testable code.

Video:

Why RabbitMQ:

• Decouple message publisher and consumer
• Store the messages
• Routing of messages
• Monitoring and management of messages

SpringBoot RabbitMQ Diagram

Producer:

In this spring boot module, We will config rabbitMQ details including exchange, queue and we will send message to queue.

Exchange:

We will create one exchange and send message to this exchange.

Routing :

We will create routing key and bind exchange with specific queue with routing key.

Queue:

Here, our message will be stored. Once consumed by consumers, message will be removed from queue.

RabbitMQ Configuration in spring boot:

application.properties

server.port=8001

#Rabbitmq configuration

spring.rabbitmq.host = 127.0.0.1

spring.rabbitmq.port = 5672

spring.rabbitmq.username = guest

spring.rabbitmq.password = guest

RobbitMqConfig.java

package com.sachin4java.rabbitmqproducer.config;

import org.springframework.amqp.core.Binding;

import org.springframework.amqp.core.BindingBuilder;

import org.springframework.amqp.core.Queue;

import org.springframework.amqp.core.TopicExchange;

import org.springframework.amqp.rabbit.connection.ConnectionFactory;

import org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer;

import org.springframework.amqp.rabbit.listener.adapter.MessageListenerAdapter;

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.Configuration;

import com.sachin4java.rabbitmqproducer.listener.MessageListener;

@Configuration

public class RobbitMqConfig {

public static final String ROUTING_KEY = "my.queue.key";

@Bean

Queue queue() {

return new Queue(ROUTING_KEY, true);

}

@Bean

TopicExchange exchange() {

return new TopicExchange("my_queue_exchange");

}

@Bean

Binding binding(Queue queue, TopicExchange exchange) {

return BindingBuilder.bind(queue).to(exchange).with(ROUTING_KEY);

}

//Below highlighted for RabbitMQ listener

@Bean

SimpleMessageListenerContainer container(ConnectionFactory connectionFactory,

MessageListenerAdapter listenerAdapter) {

SimpleMessageListenerContainer container = new SimpleMessageListenerContainer();

container.setConnectionFactory(connectionFactory);

container.setQueueNames(ROUTING_KEY);

container.setMessageListener(listenerAdapter);

return container;

}

@Bean

MessageListenerAdapter myQueueListener(MessageListener listener) {

return new MessageListenerAdapter(listener, "onMessage");

}

}

Module name	Port	Type	Dependencies
rabbitmq-producer	8001	Sender	Web, AMQP
rabbitmq-consumer	8002	Receiver	Web, AMQP

Rabbitmq-producer module:

ProducerController.java

package com.sachin4java.rabbitmqproducer.controller;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.web.bind.annotation.GetMapping;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RequestParam;

import org.springframework.web.bind.annotation.RestController;

import com.sachin4java.rabbitmqproducer.producer.MessageProducer;

@RestController

@RequestMapping("/producer")

public class ProducerController {

@Autowired

   private MessageProducer messageProducer;

   

@GetMapping

public void produce(@RequestParam String message) {

messageProducer.sendMessage(message);

   

}

}

MessageProducer.java

package com.sachin4java.rabbitmqproducer.producer;

import java.util.Date;

import org.springframework.amqp.rabbit.core.RabbitTemplate;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.stereotype.Component;

import com.sachin4java.rabbitmqproducer.config.RobbitMqConfig;

@Component

public class MessageProducer {

@Autowired

   private RabbitTemplate rabbitTemplate;

public void sendMessage(String message) {

System.out.println(new Date());

rabbitTemplate.convertAndSend(RobbitMqConfig.ROUTING_KEY, message);

   System.out.println("Is listener returned ::: "+rabbitTemplate.isReturnListener());

   System.out.println(new Date());

}

}

RobbitMqConfig.java

package com.sachin4java.rabbitmqproducer.config;

import org.springframework.amqp.core.Binding;

import org.springframework.amqp.core.BindingBuilder;

import org.springframework.amqp.core.Queue;

import org.springframework.amqp.core.TopicExchange;

import org.springframework.amqp.rabbit.connection.ConnectionFactory;

import org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer;

import org.springframework.amqp.rabbit.listener.adapter.MessageListenerAdapter;

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.Configuration;

import com.sachin4java.rabbitmqproducer.listener.MessageListener;

@Configuration

public class RobbitMqConfig {

public static final String ROUTING_KEY = "my.queue.key";

@Bean

Queue queue() {

return new Queue(ROUTING_KEY, true);

}

@Bean

TopicExchange exchange() {

return new TopicExchange("my_queue_exchange");

}

@Bean

Binding binding(Queue queue, TopicExchange exchange) {

return BindingBuilder.bind(queue).to(exchange).with(ROUTING_KEY);

}

/*@Bean

SimpleMessageListenerContainer container(ConnectionFactory connectionFactory,

MessageListenerAdapter listenerAdapter) {

SimpleMessageListenerContainer container = new SimpleMessageListenerContainer();

container.setConnectionFactory(connectionFactory);

container.setQueueNames(ROUTING_KEY);

container.setMessageListener(listenerAdapter);

return container;

}

@Bean

MessageListenerAdapter myQueueListener(MessageListener listener) {

return new MessageListenerAdapter(listener, "onMessage");

}*/

}

Rabbitmq-consumer module:

RobbitMqConfig.java

package com.sachin4java.rabbitmqproducer.config;

import org.springframework.amqp.core.Binding;

import org.springframework.amqp.core.BindingBuilder;

import org.springframework.amqp.core.Queue;

import org.springframework.amqp.core.TopicExchange;

import org.springframework.amqp.rabbit.connection.ConnectionFactory;

import org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer;

import org.springframework.amqp.rabbit.listener.adapter.MessageListenerAdapter;

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.Configuration;

import com.sachin4java.rabbitmqproducer.listener.MessageListener;

@Configuration

public class RobbitMqConfig {

public static final String ROUTING_KEY = "my.queue.key";

@Bean

Queue queue() {

return new Queue(ROUTING_KEY, true);

}

@Bean

TopicExchange exchange() {

return new TopicExchange("my_queue_exchange");

}

@Bean

Binding binding(Queue queue, TopicExchange exchange) {

return BindingBuilder.bind(queue).to(exchange).with(ROUTING_KEY);

}

@Bean

SimpleMessageListenerContainer container(ConnectionFactory connectionFactory,

MessageListenerAdapter listenerAdapter) {

SimpleMessageListenerContainer container = new SimpleMessageListenerContainer();

container.setConnectionFactory(connectionFactory);

container.setQueueNames(ROUTING_KEY);

container.setMessageListener(listenerAdapter);

return container;

}

@Bean

MessageListenerAdapter myQueueListener(MessageListener listener) {

return new MessageListenerAdapter(listener, "onMessage");

}

}

MessageListener.java

package com.sachin4java.rabbitmqproducer.listener;

public interface MessageListener {

public void onMessage(String message);

}

MessageListenerImpl.java

package com.sachin4java.rabbitmqproducer.listener;

import java.util.Date;

import org.springframework.stereotype.Component;

@Component

public class MessageListenerImpl implements MessageListener{

@Override

public void onMessage(String message) {

System.out.println(new Date());

try {

Thread.sleep(5000);

} catch (InterruptedException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

System.out.println("Message Received:"+message);

System.out.println(new Date());

}

}

GIT Repository

Rabbitmq-producer -  https://github.com/ranesaci/rabbitmq-producer.git

Rabbitmq-consumer - https://github.com/ranesaci/rabbitmq-consumer.git