In computing, an application programming interface is an interface that defines interactions between multiple software applications or mixed hardware-software intermediaries.

What Is an Example of an API?

When you use an application on your mobile phone, the application connects to the Internet and sends data to a server. The server then retrieves that data, interprets it, performs the necessary actions and sends it back to your phone. The application then interprets that data and presents you with the information you wanted in a readable way. This is what an API is - all of this happens via API.

To explain this better, let us take a familiar example.

Imagine you’re sitting at a table in a restaurant with a menu of choices to order from. The kitchen is the part of the “system” that will prepare your order. What is missing is the critical link to communicate your order to the kitchen and deliver your food back to your table. That’s where the waiter or API comes in. The waiter is the messenger – or API – that takes your request or order and tells the kitchen – the system – what to do. Then the waiter delivers the response back to you; in this case, it is the food.

 FlowChart

Symbol	Purpose	Description
	Flow line	Indicates the flow of logic by connecting symbols.
	Terminal(Stop/Start)	Represents the start and the end of a flowchart.
	Input/Output	Used for input and output operation.
	Processing	Used for arithmetic operations and data-manipulations.
	Decision	Used for decision making between two or more alternatives.
	On-page Connector	Used to join different flowline
	Off-page Connector	Used to connect the flowchart portion on a different page.
	Predefined Process/Function	Represents a group of statements performing one processing task.

Signal is on growth.

 What is Java?

• Platform independent - We can write Java code in one platform (operating system) and run on another platform without any modification.
• Object-oriented - Java is an object-oriented language. This helps to make our Java code more flexible and reusable.
• Speed - Well optimized Java code is nearly as fast as lower-level languages like C++ and much faster than Python, PHP, etc.

Why Learn Java?

• Java is a platform-independent language. We can write Java code in one platform and run it in another platform
• Java is a general-purpose language with a wide range of applications. It's used for developing mobile and desktop applications, big data processing, embedded systems, and so on.
• Java is an object-oriented programming language. It helps in code reusability.

JOB ROLES FOR JAVA DEVELOPERS:

• Software Developer – C
• Programmer Analyst – C
• C Consultant
• Software Engineer – C++
• Embedded Developer – OOPS
• Module Lead – Core Java
• Sr Developer – Core Java
• Software Engineer – Core Java
• Core Java Developer
• Architect – Core Java
• Software Engineer – JSP
• Application Developer – JSP
• Software Engineer – Servlets
• UI Developer – JS
• IoT Software Engineer
• Lead Developer – Angular JS

How to Print an Integer entered by an user

import java.util.Scanner;

public class HelloWorld {

    public static void main(String[] args) {

        // Creates a reader instance which takes
        // input from standard input - keyboard
        Scanner reader = new Scanner(System.in);
        System.out.print("Enter a number: ");

        // nextInt() reads the next integer from the keyboard
        int number = reader.nextInt();

        // println() prints the following line to the output screen
        System.out.println("You entered: " + number);
    }
}

Program to Add Two Integers

public class AddTwoIntegers {

    public static void main(String[] args) {
        
        int first = 10;
        int second = 20;

        System.out.println("Enter two numbers: " + first + " " + second);
        int sum = first + second;

        System.out.println("The sum is: " + sum);
    }
}

Check whether a number is even or odd using if...else statement

import java.util.Scanner;

public class EvenOdd {

    public static void main(String[] args) {

        Scanner reader = new Scanner(System.in);

        System.out.print("Enter a number: ");
        int num = reader.nextInt();

        if(num % 2 == 0)
            System.out.println(num + " is even");
        else
            System.out.println(num + " is odd");
    }
}

 What is Python?

Python is a cross-platform programming language, which means that it can run on multiple platforms like Windows, macOS, Linux, and has even been ported to the Java and .NET virtual machines. It is free and open-source.

# This program prints Hello, world!

print('Hello, world!')

# This program adds two numbers

num1 = 1.5
num2 = 6.3

# Add two numbers
sum = num1 + num2

# Display the sum
print('The sum of {0} and {1} is {2}'.format(num1, num2, sum))

# Python program to swap two variables

x = 5
y = 10

# To take inputs from the user
#x = input('Enter value of x: ')
#y = input('Enter value of y: ')

# create a temporary variable and swap the values
temp = x
x = y
y = temp

print('The value of x after swapping: {}'.format(x))
print('The value of y after swapping: {}'.format(y))

Kilometers to Miles

# Taking kilometers input from the user
kilometers = float(input("Enter value in kilometers: "))

# conversion factor
conv_fac = 0.621371

# calculate miles
miles = kilometers * conv_fac
print('%0.2f kilometers is equal to %0.2f miles' %(kilometers,miles))