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Dependency Injection in Spring framework

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Before understanding Dependency Injection(DI) in Spring framework, I recommend you to understand Dependency Injection design pattern As explained in above link, Dependency Injection is a design pattern in which object's properties are set by external entity. External entity can be simple java class which configure object's properties. Spring core (IoC) container acts as external entity to configure object's properties. There are 2 ways in Spring framework to achieve DI. 1. Setter Injection 2. Constructor Injection Let's write simple example to understand DI in Spring framework. We will set primitive values in Employee class using setter injection. I have used maven to add Spring framework related jars. You can add these external jars in eclipse by right click on project --> Build Path --> Configure Build Path... --> Add external JARs --> select jar --> Ok.  Project Structure:  POM.xml:  <project xmlns:xsi="http://www.w3.org/...
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equals() method of Object class in Java

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When you compare two object references using == operator, it evaluate to true only when both references refer to same object. public class Person { private Integer id; private String name; public Person(Integer id, String name) { this.id = id; this.name = name; } public static void main(String[] args) { Person p1 = new Person(1, "Prithvi"); Person p2 = p1; Person p3= new Person(1, "Prithvi"); System.out.println(p1==p2); System.out.println(p1==p3); } } Output: true false We have created 3 references of Person class. Object references p1 and p2 both refer to same object so comparison evaluate to true. Comparison of p1 and p3 evaluate to false, even though p3 has same contents as p1 but refer to different object so comparison returns false. Below image explains this - Objects p3 and p1 are meaningfully equal. We must have some way to see their content are same or not. But the question is, How will you compare two different object...
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How to define Auxiliary Constructor in case class in Scala

We have seen case class previously. We had discussed what is case class, how to create object of case class, list of boilerplate code generated for case class. If you don't know case class, I recommend to understand case class first. Let us revise case class declaration. case class Person(id:Int, name: String) Person class is declared with primary constructor where id and name are parameter. So good so far. The constructor which is not primary constructor, other than primary constructors and overloaded to primary constructor are called auxiliary constructor. How will you declare Auxiliary(other overloaded) constructors. What is syntax of creating auxiliary constructor. Please note that constructors in case class are not really constructor. Actually these are apply methods on companion object. Auxiliary constructor in case class are different than regular class. We can add auxiliary constructors in case class by adding apply() methods in companion object of case class...
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