"Java Basics Unveiled: A Comprehensive Guide to Variables, Data Types, and Basic Operations"?

Chapter 1: Variables and Data Types in Java

Java is a powerful programming language widely used for building various applications. In this chapter, we will explore some fundamental concepts such as creating a Java file, understanding boilerplate code, and working with variables and data types. We'll also cover basic input/output operations, mathematical operations, and assignments.

1. Creating a Java File

To start coding in Java, the first step is to create a Java file. A Java file is simply a text file with the .java extension. The file name should match the class name. For example, if your class is named Hello_World, the file should be saved as Hello_World.java.

2. Boilerplate Code

Java programs require a specific structure or "boilerplate code" to run. This includes defining a class and the main method, which serves as the entry point of the program.

public class Hello_World {
    public static void main(String[] args) {
        System.out.println("Hello World!");
    }
}

• Class Declaration: The public class Hello_World line declares a class named Hello_World.

• Main Method: The public static void main(String[] args) method is where the program execution begins. The System.out.println("Hello World!"); statement prints "Hello World!" to the console.

3. Output in Java

The System.out.println() function is used to print text to the console. For example:

System.out.println("Hello World!");

This will output Hello World! on the console.

4. Print a Pattern

You can use the System.out.println() function to print patterns. Here's an example of printing a triangle pattern:

public class PrintTriangle {
    public static void main(String[] args) {
        System.out.println("****");
        System.out.println("***");
        System.out.println("**");
        System.out.println("*");
    }
}

This code will output:

****
***
**
*

5. Variables in Java

Variables are used to store data in a Java program. You can declare and initialize variables like this:

public class Variable {
    public static void main(String[] args) {
        int a = 5;
        int b = 9;
        System.out.println(a); // Output: 5
        String name = "Rohit Gawande";
        System.out.print(name); // Output: Rohit Gawande
    }
}

• int: Stores integers (whole numbers) without decimals.

• String: Stores a sequence of characters, like a word or sentence.

6. Data Types in Java

Java is a statically typed language, meaning each variable must have a data type.Java has various data types to store different kinds of data:

• Primitive Data Types: These include int (integer), float (floating-point number), char (character), boolean (true/false), etc.

• Non-Primitive Data Types: These include String, arrays, classes, etc.

Here's a summary of primitive data types:

7. Sum of Two Numbers

Let's write a simple program to calculate the sum of two numbers:

public class Sum {
    public static void main(String[] args) {
        int a = 8;
        int b = 7;
        int sum = a + b;
        System.out.println(sum); // Output: 15
    }
}

8. Comments in Java

Comments are used to explain code and are ignored by the compiler. There are two types:

• Single-line comments: Start with //

• Multi-line comments: Enclosed in /* */

Example:

// This is a single-line comment
/* This is a 
   multi-line comment */

9. Input in Java

Java uses the Scanner class to take input from the user. Here's how you can use it:

import java.util.Scanner;

public class InputSum {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter a:");
        int a = sc.nextInt();
        System.out.println("Enter b:");
        int b = sc.nextInt();
        int sum = a + b;
        System.out.println("The sum of a and b: " + sum);
    }
}

• Scanner sc = new Scanner(System.in); initializes the scanner to take input from the user.

• nextInt() reads an integer from the user.

10. Product of Two Numbers

Similarly, you can calculate the product of two numbers using input from the user:

import java.util.Scanner;

public class Prod {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter a:");
        int a = sc.nextInt();
        System.out.println("Enter b:");
        int b = sc.nextInt();
        int mul = a * b;
        System.out.println("The product of a and b: " + mul);
    }
}

11. Area of a Circle

To calculate the area of a circle, you can use the formula πr^2 where r is the radius:

import java.util.Scanner;

public class CircleArea {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter radius:");
        float radius = sc.nextFloat();
        float area = 3.14f * radius * radius;
        System.out.println("Area of Circle: " + area);
    }
}

12. Type Conversion

Type conversion allows converting one data type to another. For example:

int a = 10;
float b = a; // Automatic type conversion from int to float

13. Type Casting

Type casting is explicitly converting one data type to another, like converting a float to an int:

public class TypeCasting {
    public static void main(String[] args) {
        int a = 10;
        float b = 5.0f;
        int c = (int) b; // Narrowing conversion from float to int
        System.out.println(c); // Output: 5
    }
}

14. Type Promotion in Expressions

Java automatically promotes lower data types to higher ones in expressions. For example:

public class TypePromotion {
    public static void main(String[] args) {
        byte b = 42;
        char c = 'a';
        short s = 1024;
        int i = 50000;
        float f = 5.67f;
        double d = .1234;
        double result = (f * b) + (i / c) - (d * s);
        System.out.println(result);
    }
}

In this example, all smaller data types are promoted to the largest type in the expression, which is double.

15. How Does Java Code Run?

Java code goes through several stages to execute:

• Writing Code: Code is written in a .java file.

• Compilation: The Java compiler (javac) converts the code into bytecode, a platform-independent code stored in a .class file.

• Execution: The Java Virtual Machine (JVM) executes the bytecode on the platform.

Assignments

1. Calculate the Average of Three Numbers:

import java.util.Scanner;

public class Q1 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter a:");
        int a = sc.nextInt();
        System.out.println("Enter b:");
        int b = sc.nextInt();
        System.out.println("Enter c:");
        int c = sc.nextInt();
        int average = (a + b + c) / 3;
        System.out.println("The Average of 3 numbers is: " + average);
    }
}

2. Calculate the Area of a Square:

import java.util.Scanner;

public class Q2 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter side:");
        float side = sc.nextFloat();
        float area = side * side;
        System.out.println("Area of Square is: " + area);
    }
}

3. Calculate the Total Cost of Items:

import java.util.Scanner;

public class Q3 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter the price of Pen:");
        float pen = sc.nextFloat();
        System.out.println("Enter the price of Pencil:");
        float pencil = sc.nextFloat();
        System.out.println("Enter the price of Eraser:");
        float eraser = sc.nextFloat();
        float total = pen + pencil + eraser;
        System.out.println("Bill: " + total);
        float totalGST = total + (0.18f * total);
        System.out.println("Bill with GST: " + totalGST);
    }
}

Conclusion:

In this chapter, we covered the basics of Java, including creating Java files, understanding the boilerplate code, working with variables and data types, and solving basic problems using these concepts. Mastering these fundamentals is essential as you move forward in your journey of learning Java with DSA.

Stay tuned for the next chapter, where we’ll dive deeper into more complex topics and continue building our Java programming skills. Happy coding!

Rohit Gawande