Introduction to Microservice Architecture Using SpringBoot - Part 1

JAVA Package

A java package is a group of similar types of classes, interfaces and sub-packages.

Package in java can be categorized in two form, built-in package and user-defined package.

There are many built-in packages such as java, lang, awt, javax, swing, net, io, util, sql etc.

Advantage of Java Package

1) Java package is used to categorize the classes and interfaces so that they can be easily maintained.

2) Java package provides access protection.

3) Java package removes naming collision.

Access Modifiers in Java

There are four types of Java access modifiers:

Private: The access level of a private modifier is only within the class. It cannot be accessed from outside the class.

Default: The access level of a default modifier is only within the package. It cannot be accessed from outside the package. If you do not specify any access level, it will be the default.

Protected: The access level of a protected modifier is within the package and outside the package through child class. If you do not make the child class, it cannot be accessed from outside the package.

Public: The access level of a public modifier is everywhere. It can be accessed from within the class, outside the class, within the package and outside the package.

Interface in Java

Interface in Java

An interface in Java is a blueprint of a class. It has static constants and abstract methods.

The interface in Java is a mechanism to achieve abstraction. There can be only abstract methods in the Java interface, not method body. It is used to achieve abstraction and multiple inheritance in Java.

Java Interface also represents the IS-A relationship.

How to declare an interface?

An interface is declared by using the interface keyword.

Why use Java interface?

There are mainly three reasons to use interface. They are given below.

It is used to achieve abstraction. By interface, we can support the functionality of multiple inheritance.

It can be used to achieve loose coupling.

What is Dynamic Method Lookup?

Dynamic method lookup is the process of determining which method definition a method signature denotes during runtime, based on the type of the object. However, a call to a private instance method is not polymorphic. Such a call can only occur within the class, and gets bound to the private method implementation at compile time.