ii-Core-Java-Syntax.md

☕ Core Java Syntax & Fundamentals

This section covers the essential building blocks of Java programming, including variables, input/output, operators, control flow, and arrays.

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1. Java Data Types

Data types define the size and type of values that can be stored in a variable.

Data Type	Default Value	Size	Range / Details
boolean	false	1 bit	true or false
byte	0	1 byte (8 bit)	-128 to 127
short	0	2 bytes (16 bit)	-32,768 to 32,767
int	0	4 bytes (32 bit)	-2³¹ to 2³¹ - 1
long	0L	8 bytes (64 bit)	-2⁶³ to 2⁶³ - 1
float	0.0f	4 bytes (32 bit)	up to 7 decimal digits
double	0.0d	8 bytes (64 bit)	up to 16 decimal digits
char	'\u0000'	2 bytes (16 bit)	'\u0000' to '\uffff'

🧠 Why is char 2 Bytes in Java?

Unlike C/C++ (where char is 1 byte), Java uses the Unicode system to support a wide range of international characters. The 2-byte size allows Java to support 65,536 unique characters, covering alphabets, symbols, and special characters from many languages (English, Hindi, Chinese, Japanese, etc.).

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2. Basic Program Structure & Output

The main Method

Every Java program must have a main class and a main method to run. The class name and the filename must match.

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

Printing to the Console

• System.out.print(): Prints on the same line.
• System.out.println(): Prints and moves the cursor to the next line.

String Concatenation Rules:

int x = 10, y = 20;

System.out.println("The numbers are " + x + " and " + y); // Output: The numbers are 10 and 20
System.out.println("" + x + y);                         // Output: 1020 (treats as strings)
System.out.println(x + y + "");                         // Output: 30 (adds first, then converts to string)
System.out.println((x + y));                            // Output: 30

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3. Taking User Input (Scanner Class)

To take input from the user, we use the Scanner class from the java.util package.

import java.util.Scanner;

public class InputExample {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        System.out.print("Enter a string: ");
        String s = sc.nextLine();

        System.out.print("Enter an integer: ");
        int num = sc.nextInt();

        System.out.print("Enter a float: ");
        float f = sc.nextFloat();
        
        System.out.println("String: " + s + ", Int: " + num + ", Float: " + f);
    }
}

💻 Practice Question: Basic Calculator

Create a class named Calculator. Take two int values as user input and perform addition, subtraction, multiplication, and division.

import java.util.Scanner;

public class Calculator {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        System.out.print("Enter first number: ");
        int num1 = sc.nextInt();
        
        System.out.print("Enter second number: ");
        int num2 = sc.nextInt();
        
        System.out.println("Addition: " + (num1 + num2));
        System.out.println("Subtraction: " + (num1 - num2));
        System.out.println("Multiplication: " + (num1 * num2));
        System.out.println("Division: " + (num1 / num2));
    }
}

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4. Java Operators

Operators are symbols used to perform operations on variables and values. Java mainly has 8 types:

1. Unary: +, -, ++, --, !
2. Arithmetic: +, -, *, /, %
3. Relational: ==, !=, <, >, <=, >=
4. Bitwise: &, |, ^, ~
5. Shift: <<, >>, >>>
6. Logical: &&, ||, !
7. Assignment: =, +=, -=, *=, /=, %=
8. Ternary: condition ? true_value : false_value;

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5. Conditional Statements

Used to make decisions in code based on boolean conditions.

• if statement: Executes a block of code if a condition is true.
• if-else statement: Executes one block if true, another if false.
• if-else-ladder: Checks multiple conditions sequentially.
• switch statement: Selects one of many code blocks to be executed based on a variable's value.

switch (expression) {
    case value1:
        // code block
        break;
    case value2:
        // code block
        break;
    default:
        // default code block
}

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6. Loops in Java

Loops are used to execute a block of code multiple times.

1. for loop: for(initialization; condition; increment/decrement) { ... }
2. while loop: while(condition) { ... }
3. do-while loop: Executes the code at least once before checking the condition.
4. for-each loop: Specifically used to iterate over arrays or collections.
   • for(dataType variableName : arrayName) { ... }

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7. Arrays in Java

An array is a collection of elements of the same datatype stored in contiguous memory locations.

Array Syntax & Initialization

// Method 1: Declaration and Memory Allocation
int[] arr1 = new int[5];

// Method 2: With predefined values
int[] arr2 = {10, 20, 30, 40, 50};

// Method 3: Dynamic size allocation
int n = 7;
int[] arr3 = new int[n]; 

💻 Taking Array Input and Printing It

Here is how you populate an array using Scanner and print its contents using a loop:

import java.util.Scanner;

public class ArrayExample {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        System.out.print("Enter the number of elements: ");
        int n = sc.nextInt();
        
        int[] a = new int[n]; // Create array of size n
        
        System.out.println("Enter the elements:");
        for(int i = 0; i < n; i++) {
            a[i] = sc.nextInt(); // Take input for each index
        }
        
        System.out.println("The array elements are:");
        for(int i = 0; i < a.length; i++) {
            System.out.print(a[i] + " "); // Print each element
        }
    }
}