import java.util.Arrays; import java.util.Date; /** * JavaExamplesDemo - Comprehensive demonstration of Java programming concepts * * This class contains practical examples covering: * - Mathematical algorithms and approximations * - Array operations and statistical calculations * - Object-oriented programming with inheritance * - String manipulation and data processing */ public class JavaExamplesDemo { // ============================================================================ // MATHEMATICAL ALGORITHMS // ============================================================================ /** * Calculates the largest integer k where k^2 <= n * @param n the input number * @return the integer square root */ public static int integerSquareRoot(int n) { int k = 0; while ((k + 1) * (k + 1) <= n) { k++; } return k; } /** * Approximates pi using the Leibniz series * pi = 4(1 - 1/3 + 1/5 - 1/7 + ... + 1/(2i-1) - 1/(2i+1)) * @param iterations number of terms in the series * @return approximation of pi */ public static double piApproximation(int iterations) { double pi = 1; for (int i = 1; i < iterations; i++) { if (i % 2 != 0) { pi -= (1.0 / (2 * i + 1)); } else { pi += (1.0 / (2 * i + 1)); } } return 4 * pi; } /** * Calculates factorial using iteration * @param n the number * @return n! (factorial of n) */ public static long factorial(int n) { long result = 1; for (int i = 2; i <= n; i++) { result *= i; } return result; } // ============================================================================ // ARRAY OPERATIONS AND STATISTICS // ============================================================================ /** * Calculates the standard deviation of an array of numbers * @param numbers array of values * @return standard deviation */ public static double standardDeviation(double[] numbers) { if (numbers == null || numbers.length == 0) { return 0.0; } // Calculate mean double sum = 0; for (double num : numbers) { sum += num; } double mean = sum / numbers.length; // Calculate variance double variance = 0; for (double num : numbers) { variance += Math.pow(num - mean, 2); } variance /= numbers.length; return Math.sqrt(variance); } /** * Finds the maximum value in an array * @param numbers array of values * @return maximum value */ public static double findMax(double[] numbers) { if (numbers == null || numbers.length == 0) { throw new IllegalArgumentException("Array cannot be empty"); } double max = numbers[0]; for (int i = 1; i < numbers.length; i++) { if (numbers[i] > max) { max = numbers[i]; } } return max; } /** * Finds the minimum value in an array * @param numbers array of values * @return minimum value */ public static double findMin(double[] numbers) { if (numbers == null || numbers.length == 0) { throw new IllegalArgumentException("Array cannot be empty"); } double min = numbers[0]; for (int i = 1; i < numbers.length; i++) { if (numbers[i] < min) { min = numbers[i]; } } return min; } /** * Reverses an array in place * @param arr array to reverse */ public static void reverseArray(int[] arr) { int left = 0; int right = arr.length - 1; while (left < right) { int temp = arr[left]; arr[left] = arr[right]; arr[right] = temp; left++; right--; } } // ============================================================================ // STRING OPERATIONS // ============================================================================ /** * Checks if a string is a palindrome * @param str input string * @return true if palindrome, false otherwise */ public static boolean isPalindrome(String str) { if (str == null || str.isEmpty()) { return true; } String cleaned = str.toLowerCase().replaceAll("[^a-z0-9]", ""); int left = 0; int right = cleaned.length() - 1; while (left < right) { if (cleaned.charAt(left) != cleaned.charAt(right)) { return false; } left++; right--; } return true; } /** * Counts vowels in a string * @param str input string * @return number of vowels */ public static int countVowels(String str) { if (str == null || str.isEmpty()) { return 0; } int count = 0; String vowels = "aeiouAEIOU"; for (char c : str.toCharArray()) { if (vowels.indexOf(c) != -1) { count++; } } return count; } // ============================================================================ // GEOMETRIC OBJECT CLASSES (OOP DEMONSTRATION) // ============================================================================ /** * Base class for geometric objects demonstrating inheritance */ public static class GeometricObject { private String color; private boolean filled; private Date dateCreated; public GeometricObject() { this.color = "white"; this.filled = false; this.dateCreated = new Date(); } public GeometricObject(String color, boolean filled) { this.color = color; this.filled = filled; this.dateCreated = new Date(); } public String getColor() { return color; } public void setColor(String color) { this.color = color; } public boolean isFilled() { return filled; } public void setFilled(boolean filled) { this.filled = filled; } public Date getDateCreated() { return dateCreated; } @Override public String toString() { return "Created on " + dateCreated + "\nColor: " + color + "\nFilled: " + filled; } } /** * Circle class extending GeometricObject */ public static class Circle extends GeometricObject { private double radius; public Circle() { this.radius = 1.0; } public Circle(double radius) { this.radius = radius; } public Circle(double radius, String color, boolean filled) { super(color, filled); this.radius = radius; } public double getRadius() { return radius; } public void setRadius(double radius) { this.radius = radius; } public double getArea() { return Math.PI * radius * radius; } public double getPerimeter() { return 2 * Math.PI * radius; } @Override public String toString() { return "Circle: radius=" + radius + "\n" + super.toString(); } } /** * Rectangle class extending GeometricObject */ public static class Rectangle extends GeometricObject { private double width; private double height; public Rectangle() { this.width = 1.0; this.height = 1.0; } public Rectangle(double width, double height) { this.width = width; this.height = height; } public Rectangle(double width, double height, String color, boolean filled) { super(color, filled); this.width = width; this.height = height; } public double getWidth() { return width; } public void setWidth(double width) { this.width = width; } public double getHeight() { return height; } public void setHeight(double height) { this.height = height; } public double getArea() { return width * height; } public double getPerimeter() { return 2 * (width + height); } @Override public String toString() { return "Rectangle: width=" + width + ", height=" + height + "\n" + super.toString(); } } // ============================================================================ // MAIN METHOD - DEMONSTRATION // ============================================================================ public static void main(String[] args) { System.out.println("╔════════════════════════════════════════════════════════╗"); System.out.println("║ Java Programming Examples Demonstration ║"); System.out.println("╚════════════════════════════════════════════════════════╝\n"); // Mathematical Algorithms System.out.println("═══ MATHEMATICAL ALGORITHMS ═══\n"); int num = 50; System.out.println("Integer square root of " + num + ": " + integerSquareRoot(num)); System.out.println("Expected: 7 (since 7² = 49 ≤ 50 < 8² = 64)\n"); int iterations = 1000000; System.out.println("Pi approximation (" + iterations + " iterations): " + piApproximation(iterations)); System.out.println("Actual value of Pi: " + Math.PI + "\n"); int factNum = 10; System.out.println("Factorial of " + factNum + ": " + factorial(factNum) + "\n"); // Array Operations System.out.println("═══ ARRAY OPERATIONS & STATISTICS ═══\n"); double[] testData = {12.5, 15.3, 18.7, 22.1, 14.9, 16.8, 20.3}; System.out.println("Test data: " + Arrays.toString(testData)); System.out.printf("Standard deviation: %.4f%n", standardDeviation(testData)); System.out.printf("Maximum value: %.2f%n", findMax(testData)); System.out.printf("Minimum value: %.2f%n\n", findMin(testData)); int[] reverseTest = {1, 2, 3, 4, 5}; System.out.println("Before reverse: " + Arrays.toString(reverseTest)); reverseArray(reverseTest); System.out.println("After reverse: " + Arrays.toString(reverseTest) + "\n"); // String Operations System.out.println("═══ STRING OPERATIONS ═══\n"); String[] testStrings = {"racecar", "hello", "A man, a plan, a canal: Panama"}; for (String str : testStrings) { System.out.println("\"" + str + "\" is " + (isPalindrome(str) ? "" : "NOT ") + "a palindrome"); } System.out.println(); String vowelTest = "Hello World Programming"; System.out.println("\"" + vowelTest + "\" contains " + countVowels(vowelTest) + " vowels\n"); // Object-Oriented Programming System.out.println("═══ OBJECT-ORIENTED PROGRAMMING ═══\n"); Circle circle = new Circle(5.0, "red", true); System.out.println(circle); System.out.printf("Area: %.2f%n", circle.getArea()); System.out.printf("Perimeter: %.2f%n\n", circle.getPerimeter()); Rectangle rectangle = new Rectangle(4.0, 6.0, "blue", false); System.out.println(rectangle); System.out.printf("Area: %.2f%n", rectangle.getArea()); System.out.printf("Perimeter: %.2f%n\n", rectangle.getPerimeter()); System.out.println("╔════════════════════════════════════════════════════════╗"); System.out.println("║ Demonstration Complete! ║"); System.out.println("╚════════════════════════════════════════════════════════╝"); } }