/** * Examples from Chapter 6. */ public class Series { public static void countup(int n) { if (n == 0) { System.out.println("Blastoff!"); } else { countup(n - 1); System.out.println(n); } } public static double calculateArea(double radius) { double result = Math.PI * radius * radius; return result; } public static double calculateArea2(double radius) { return Math.PI * radius * radius; } public static double absoluteValue(double x) { if (x < 0) { return -x; } else { return x; } } public static double distance (double x1, double y1, double x2, double y2) { double dx = x2 - x1; double dy = y2 - y1; System.out.println("dx is " + dx); System.out.println("dy is " + dy); return 0.0; } public static double distance2 (double x1, double y1, double x2, double y2) { double dx = x2 - x1; double dy = y2 - y1; double dsquared = dx * dx + dy * dy; System.out.println("dsquared is " + dsquared); return 0.0; } public static double distance3 (double x1, double y1, double x2, double y2) { double dx = x2 - x1; double dy = y2 - y1; double dsquared = dx * dx + dy * dy; double result = Math.sqrt(dsquared); return result; } public static double circleArea (double xc, double yc, double xp, double yp) { double radius = distance(xc, yc, xp, yp); double area = calculateArea(radius); return area; } public static double calculateArea (double xc, double yc, double xp, double yp) { return calculateArea(distance(xc, yc, xp, yp)); } /** * Tests whether x is a single digit integer. * * @param x the integer to test * @return true if x has one digit, false otherwise */ public static boolean isSingleDigit(int x) { if (x > -10 && x < 10) { return true; } else { return false; } } public static boolean isSingleDigit2(int x) { return x > -10 && x < 10; } public static int factorial(int n) { if (n == 0) { return 1; } int recurse = factorial(n - 1); int result = n * recurse; return result; } public static int fibonacci(int n) { if (n == 1 || n == 2) { return 1; } return fibonacci(n - 1) + fibonacci(n - 2); } public static void main(String[] args) { countup(3); System.out.println("Have a nice day."); System.out.println("calculateArea"); System.out.println(calculateArea(3.0)); System.out.println("calculateArea2"); System.out.println(calculateArea2(3.0)); System.out.println("circleArea"); System.out.println(circleArea(1.0, 2.0, 4.0, 6.0)); System.out.println("calculateArea with 4 doubles"); System.out.println(calculateArea(1.0, 2.0, 4.0, 6.0)); System.out.println("absolute value"); System.out.println(absoluteValue(-2)); System.out.println("distance"); System.out.println(distance(1.0, 2.0, 4.0, 6.0)); System.out.println("distance2"); System.out.println(distance2(1.0, 2.0, 4.0, 6.0)); System.out.println("distance3"); System.out.println(distance3(1.0, 2.0, 4.0, 6.0)); System.out.println(isSingleDigit(2)); boolean bigFlag = !isSingleDigit2(17); int z = 9; if (isSingleDigit(z)) { System.out.println("z is small"); } else { System.out.println("z is big"); } System.out.println("factorial"); System.out.println(factorial(3)); System.out.println("fibonacci"); System.out.println(fibonacci(3)); } }