# Company 3

## Core Java

* Explain JVM
* Default size of JVM
* Default size of heap
* How to increase the size of heap
* What goes in the [stack](/the-tech-toolbox/question-answers/java-spring-boot.md#what-goes-in-the-stack-and-what-goes-in-the-heap-in-detail) and what goes in the heap in detail
* What is a weak reference
* What is a weak-hashmap
* How does GC work
* How to invoke GC
* What is the finalize method and in which class does it belong to
* Is the Object class an abstract class
* Difference between vector and arraylist and which is faster
* Stack and queue
* Queue implementations
* Explain the concurrency package and what has been added
* What is latchcount
* What is a cyclic barrier
* What is an atomic integer
* What is volatile
* What is serialization, what is transient
* What is callable and how is it different from runnable
* What is the executor framework and how many types are there
* What is a future object

## Miscellaneous

* What messaging have you worked on (e.g. JMS, RabbitMQ, etc.)
* What databases have you worked on
* Can there be two JVMs on a single machine

## AWS

* What services do you know in AWS
* What database is used in AWS
* Writing stored procedures

## Java 8

* What is a functional interface
* What is the Optional class
* What is the Stream API
* Why is the Stream API lazy
* Writing a lambda expression to create a thread and print your name
* Output of the following programs:

```java
List<Integer> numbers = Arrays.asList(1,2,3);
numbers.stream().filter(n -> {
  System.out.printf("Filtering => %d \n", n);
  return n%2 == 0;
});
```

<pre class="language-java"><code class="lang-java"><strong>List&#x3C;Integer> numbers = Arrays.asList(1,2,3);
</strong>numbers.stream().filter(n -> {
  System.out.printf("Filtering => %d \n", n);
  return n%2 == 0;
}).map(n -> {
  System.out.printf("Mapping => %d \n", n);
  return n * 2;
});
</code></pre>

```java
public class Demo {
  public static void main(String args[]) {
    int[] array = new int[10];
    printArray(array);
  }

  public void printArray(int[] array){
    for(int i : array)
      System.out.println(i);
  }
}
```

## Spring Boot

* What is the default server provided by Spring Boot (e.g. Tomcat, Netty, etc)
* What is the default underlying implementation of Spring Boot JPA
* Steps to implement security in Spring Boot
* How to change the default implementation of ORM in Spring Boot
* Difference between webservice and RESTful services
* What is JAX-RS

## Git

* What is the difference between `git pull` and `git fetch`

## Database

* What is indexing and why is it used
* What is a primary key
* Can you index a primary key
* How to write a stored procedure

## Microservices

* What is microservice architecture
* What is vertical and horizontal scaling
* How to handle failover for a database server


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