Computer science notes

 In Java, every enum type inherits several built-in methods from the java.lang.Enum class, which is the base class for all enum types. These built-in methods provide functionality such as getting the name of an enum constant, comparing enum constants, and iterating over all constants. Here are the inbuilt methods provided by the Enum class: 1. values() Description : This method returns an array of all the constants of the enum type, in the order they were declared. Syntax : public static T[] values() Example : enum Day {     MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY; } public class EnumMethodsExample {     public static void main(String[] args) {         Day[] days = Day.values();  // Get all enum constants                  // Loop through the array and print each day         for (Day day : days) {             System.out....

Actually in real project development interfaces are use to write business logic code . Also Interfaces in java are powerful tools that allow you to define a contract for what a class can do, without specifying how it does it. it means we can give method declaration in interface and what that method does actually that responsibility is given to the class which is going to implement that class. They are used for several real-world purposes like enabling polymorphism , creating loosely coupled systems , and defining common behaviors across different classes . Real-World Use of Interfaces Let's look at some practical scenarios where interfaces are commonly used: 1. Multiple Inheritance (via Interfaces):  Java doesn't support multiple inheritance with classes, but it allows multiple inheritance with interfaces. This allows a class to implement multiple interfaces, enabling it to inherit behaviors from more than one source. 2. Polymorphism: Interfaces allow you to treat different o...

 Object-Oriented Programming (OOP) is a programming paradigm based on the concept of "objects". These objects represent real-world entities and are instances of classes. OOP allows developers to structure software in a way that mimics real-world systems, making code more reusable, scalable, and maintainable. There are four primary pillars of OOP: 1. Encapsulation 2. Abstraction 3. Inheritance 4. Polymorphism Each pillar is crucial for designing robust and scalable software . 1. Encapsulation Definition: Encapsulation is the bundling of data (variables) and the methods (functions) that operate on the data into a single unit called a class. It also helps restrict access to some of the object’s components, which is known as data hiding. Real-Time Use: Consider a bank account system. We can define a class BankAccount where the balance is a private property. We expose only the necessary functionality, such as deposit and withdraw methods, to interact with the balance. Code Example...

Creating a REST API in Java can be achieved using frameworks like Spring Boot , which simplifies development and setup. Below is a detailed guide to building a REST API for managing books using Spring Boot . restVsSoap Prerequisites:      Java Development Kit (JDK) : Ensure JDK 11 or higher is installed.      Maven : Build tool for managing dependencies and building the project.      Spring Boot : A popular framework for creating RESTful services. Steps to Create a REST API 1. Setup a Spring Boot Project You can create a Spring Boot project using:      Spring Initializr      Your IDE (e.g., IntelliJ IDEA or Eclipse) Include the following dependencies:      Spring Web : For building REST APIs.      Spring Boot DevTools (Optional): For live reload during development. Maven Dependency Configuration (pom.xml)      < dependencies >   < dependency >   ...

The Factory Design Pattern in Java is a creational pattern used to encapsulate the object creation logic. It allows you to create objects without specifying the exact class name, promoting loose coupling and scalability. Real-Life Example: Consider a Shape Factory that can create different types of shapes like Circle, Rectangle, and Square. Code Implementation: Java code: // Step 1: Define a common interface for all products interface Shape { void draw () ; } // Step 2: Implement concrete classes for specific products class Circle implements Shape { @Override public void draw () { System.out.println( "Drawing a Circle" ); } } class Rectangle implements Shape { @Override public void draw () { System.out.println( "Drawing a Rectangle" ); } } class Square implements Shape { @Override public void draw () { System.out.println( "Drawing a Square" ); } } // Step 3: C...

  In Java, the equals method is a fundamental method inherited by all classes from the Object class.           Here’s an explanation of the equals method: Purpose: The equals method is used to compare two objects to determine if they are logically equivalent. By default, the implementation in the Object class checks if the two object references point to the same memory location (i.e., if they are the same instance). Signature : public boolean equals(Object obj) Explanation: Method Override: Classes can override the equals method to provide their own definition of object equality based on their specific needs. When overriding, the method should adhere to certain principles to ensure consistency and correctness of equality comparisons. Default Behavior (from Object class): The default implementation in the Object class checks if the two object references ( this and obj ) refer to the exact same object in memory using the == operator: public boo...

It is non final and concrete class available in java.lang package.  As java.lang package by default imported in all java classes there is no need to extend object class explicitly. In java all classes (not interfaces) are directly or indirectly extended from java.lang.Object class In other words java.lang.Object is ultimate base class/root class of java class hierarchy.  Object class do not extend any class or implement any interface. It does not contain nested type as well as field.  Object class contains 11 methods.  It contains default constructor Object object=new Object(); ok  Object object= new Object(“Hello”); Not Ok Consider following code:  Class Person{  }  Class Employee extends Person{  } In above code, java.lang.object is direct super class of class Person In case of class Employee, class Person is direct super class and class object is indirect super class. Methods of object class 1. public String toString();  2. p...

 Static variable: If we want to share the value of any field or variable inside all the instances of class then we should declare that variable as static. In above diagram we see that e1 and e2 are two objects of class Employee. they share the static variable companyName.  Static variables are also called as Class Variables because its copy gets shared between all the objects of same class.   Static variable gets space in method area at the time of class loading.   We can access static variables using object reference but it is designed to access using class name and dot operator.   Example:   Employee employee=new Employee(); object creation  System.out.println(“Company name:”+Employee.CompanyName): ok System.out.println(“Company name:”+employee.CompanyName): Ok  staticmethod

If we want to initialize an instance then we should define constructor inside class.  Constructor looks like method but it is not considered as method.  Constructor is special       It’s name is same as that of class name.       It does not return anything, not even void.       It is designed to be called implicitly i.e it gets called automatically when instance of the class is created.  It is called once per instance. We can not call constructor on instance explicitly.  Example:         Employee employee=new Employee();      employee.Employee(); not ok typesofconstructor

  1. Lambda Expressions A lambda expression allows you to write concise code by passing behavior as a parameter. Example: import java.util.Arrays; import java.util.List; public class LambdaExample { public static void main (String[] args) { List<String> names = Arrays.asList( "Alice" , "Bob" , "Charlie" ); // Using lambda expression names.forEach(name -> System.out.println(name)); } } 2. Stream API The Stream API provides a functional approach to process collections of data. Example: import java.util.Arrays; import java.util.List; public class StreamExample { public static void main (String[] args) { List<Integer> numbers = Arrays.asList( 1 , 2 , 3 , 4 , 5 ); // Filtering and mapping with Stream API numbers.stream() .filter(n -> n % 2 == 0 ) // Filters even numbers .map(n -> n * n) // Squares the numbers ...