☕ Java Fundamentals

public class HelloWorld {
    // Main method - entry point of the program
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

public class PrintExamples {
    public static void main(String[] args) {
        // println - prints and moves to next line
        System.out.println("Test 1: Login");
        System.out.println("Test 2: Logout");
        
        // print - prints without new line
        System.out.print("Test 3: ");
        System.out.print("Dashboard");
        System.out.println();  // Empty line
        
        // Printing numbers
        System.out.println(100);
        System.out.println(3.14);
        
        // Printing boolean
        System.out.println(true);
    }
}

// Single-line comment - use for brief explanations

/*
 * Multi-line comment
 * Use for longer explanations
 * or temporarily disabling code
 */

/**
 * JavaDoc comment - for documentation
 * @author Automation Team
 * @version 1.0
 * @since 2024-01-01
 */
public class TestRunner {
    // TODO: Add test execution logic
    public static void main(String[] args) {
        System.out.println("Running tests...");
    }
}

public class VariableExample {
    public static void main(String[] args) {
        // Declaration only
        int testCount;
        
        // Initialization
        testCount = 50;
        
        // Declaration + Initialization
        String browserName = "Chrome";
        double version = 120.5;
        boolean isHeadless = false;
        char environment = 'D';  // D = Dev, S = Stage, P = Prod
        
        // Multiple variables of same type
        int passed = 45, failed = 3, skipped = 2;
        
        // Print all variables
        System.out.println("Browser: " + browserName);
        System.out.println("Version: " + version);
        System.out.println("Total Tests: " + testCount);
        System.out.println("Passed: " + passed);
        System.out.println("Failed: " + failed);
    }
}

public class ReferenceTypes {
    public static void main(String[] args) {
        // String - most commonly used reference type
        String username = "admin@test.com";
        String password = "Test@123";
        
        // Arrays
        String[] browsers = {"Chrome", "Firefox", "Edge"};
        int[] testScores = {85, 92, 78, 95};
        
        // Print
        System.out.println("Username: " + username);
        System.out.println("First browser: " + browsers[0]);
        System.out.println("First score: " + testScores[0]);
    }
}

public class TypeCasting {
    public static void main(String[] args) {
        // Widening (Automatic) - smaller to larger type
        int testCount = 100;
        double testCountDouble = testCount;  // int → double
        System.out.println("Count as double: " + testCountDouble);  // 100.0
        
        // Narrowing (Manual) - larger to smaller type
        double percentage = 95.7;
        int rounded = (int) percentage;  // Explicit casting
        System.out.println("Rounded: " + rounded);  // 95
        
        // String to primitive conversions
        String strNumber = "123";
        int num = Integer.parseInt(strNumber);
        double decimal = Double.parseDouble("45.67");
        boolean bool = Boolean.parseBoolean("true");
        
        // Primitive to String
        int value = 456;
        String strValue = String.valueOf(value);
        String strValue2 = Integer.toString(value);
        
        System.out.println("Converted number: " + num);
        System.out.println("String value: " + strValue);
    }
}

public class Constants {
    public static void main(String[] args) {
        // Constants - cannot be changed once assigned
        final String BASE_URL = "https://example.com";
        final int MAX_RETRY_COUNT = 3;
        final int TIMEOUT_SECONDS = 30;
        
        System.out.println("Base URL: " + BASE_URL);
        System.out.println("Max Retries: " + MAX_RETRY_COUNT);
        
        // BASE_URL = "https://new-url.com";  // ❌ Error: cannot reassign
    }
}

public class ArithmeticOps {
    public static void main(String[] args) {
        int a = 20, b = 3;
        
        System.out.println("Addition: " + (a + b));        // 23
        System.out.println("Subtraction: " + (a - b));     // 17
        System.out.println("Multiplication: " + (a * b));  // 60
        System.out.println("Division: " + (a / b));        // 6 (integer division)
        System.out.println("Modulus: " + (a % b));         // 2 (remainder)
        
        // For decimal division
        double result = (double) a / b;
        System.out.println("Decimal division: " + result);  // 6.666...
        
        // Increment and Decrement
        int count = 5;
        System.out.println("count++: " + (count++));  // 5, then count becomes 6
        System.out.println("++count: " + (++count));  // 7, count increments first
        System.out.println("count--: " + (count--));  // 7, then count becomes 6
        System.out.println("--count: " + (--count));  // 5, count decrements first
    }
}

public class AssignmentOps {
    public static void main(String[] args) {
        int x = 10;
        
        x += 5;   // x = x + 5;  → 15
        System.out.println("x += 5: " + x);
        
        x -= 3;   // x = x - 3;  → 12
        System.out.println("x -= 3: " + x);
        
        x *= 2;   // x = x * 2;  → 24
        System.out.println("x *= 2: " + x);
        
        x /= 4;   // x = x / 4;  → 6
        System.out.println("x /= 4: " + x);
        
        x %= 4;   // x = x % 4;  → 2
        System.out.println("x %= 4: " + x);
    }
}

public class ComparisonOps {
    public static void main(String[] args) {
        int testsPassed = 45;
        int totalTests = 50;
        
        System.out.println(testsPassed == totalTests);  // false (equal to)
        System.out.println(testsPassed != totalTests);  // true (not equal)
        System.out.println(testsPassed > 40);          // true (greater than)
        System.out.println(testsPassed < totalTests);   // true (less than)
        System.out.println(testsPassed >= 45);         // true (greater or equal)
        System.out.println(testsPassed <= 50);         // true (less or equal)
        
        // QA Example: Check if pass rate is acceptable
        double passRate = (double) testsPassed / totalTests * 100;
        boolean acceptable = passRate >= 90.0;
        System.out.println("Pass rate: " + passRate + "%");
        System.out.println("Acceptable: " + acceptable);
    }
}

public class LogicalOps {
    public static void main(String[] args) {
        boolean isLoggedIn = true;
        boolean hasPermission = true;
        boolean isAdmin = false;
        
        // AND (&&) - both must be true
        boolean canAccess = isLoggedIn && hasPermission;
        System.out.println("Can access: " + canAccess);  // true
        
        // OR (||) - at least one must be true
        boolean canModify = isAdmin || hasPermission;
        System.out.println("Can modify: " + canModify);  // true
        
        // NOT (!) - inverts the boolean
        boolean notLoggedIn = !isLoggedIn;
        System.out.println("Not logged in: " + notLoggedIn);  // false
        
        // Complex conditions (QA example)
        int passed = 95, failed = 3, total = 100;
        boolean testSuitePassed = (failed == 0) || (passed >= 90 && total == 100);
        System.out.println("Test suite passed: " + testSuitePassed);
    }
}

public class TernaryOp {
    public static void main(String[] args) {
        // Syntax: condition ? valueIfTrue : valueIfFalse
        
        int score = 85;
        String result = (score >= 60) ? "Pass" : "Fail";
        System.out.println("Result: " + result);  // Pass
        
        // Nested ternary (be careful - can reduce readability)
        String grade = (score >= 90) ? "A" :
                      (score >= 80) ? "B" :
                      (score >= 70) ? "C" : "D";
        System.out.println("Grade: " + grade);  // B
        
        // QA Example: Set test status
        int expected = 10, actual = 10;
        String status = (expected == actual) ? "✓ PASS" : "✗ FAIL";
        System.out.println(status);
    }
}