/**

* Examples from Chapter 6.

*/

public class Series {

//standard void method

public static void countup(int n) {

if (n == 0) {

System.out.println("Blastoff!");

} else {

countup(n - 1);

System.out.println(n);

}

}

//value method, must do something with the return value

//Compared to void methods, value methods differ in two ways

//They declare the type of the return value (the return type)

//They use at least one return statement to provide a return value

//takes a double as a parameter and returns the area of a circle with a radius

public static double calculateArea(double radius) {

double result = Math.PI * radius * radius; //temporary variables make debugging easier, especially stepping through

return result; //return immediately from this method and use the following expression as the return value

}

//same function written more concisely

//note return expression must match declared return type

public static double calculateArea2(double radius) {

return Math.PI * radius * radius;

}

//multiple return statements, one in each branch of a conditional

//only one will be executed

//code that cannot be executed is called dead code

public static double absoluteValue(double x) {

if (x < 0) {

return -x;

} else {

return x;

}

System.out.println("This line is dead code.");

}

public static double absoluteValue(double x) {

if(x < 0) {

return -x;

} else if(x> 0) {

return x;

}

//syntax error - every possible path must reach a return statement

//no return path for x == 0 -error: missing return statement

//Writing Methods

//Incremental Development

//Start with a working program and make small, incremental changes.

//At any point, if there is an error, you will know where to look.

//Use variables to hold intermediate values so you can check them,

//either with print statements or by using a debugger.

//Once the program is working, you can consolidate multiple statements into

//compound expressions (but only if it does not make the program more difficult

//to read).

//Distance Formula - distance = sqrt((x2 - x1)^2 + (y2 - y1)^2))

//what are inputs? -- parameters

//what is output? -- return value

//use to make 'stub' contains method signature and a return statement

public static double distance

(double x1, double y1, double x2, double y2) {

return 0.0; //placeholder needed for program to compile.

}

//Good idea to think about testing before making methods

//in main double dist = distance(1.0,2.0,4.0,6.0);

//Horizontal distance is 3.0 and vertical 4.0, answer 5.0 (3,4,5) triangle

//helpful to know right answer

//first step - find differences of x2-x1 and y2-y1

//store in temp variables

public static double distance

(double x1, double y1, double x2, double y2) {

double dx = x2 - x1;

double dy = y2 - y1;

//remove when finished called "scaffolding"

System.out.println("dx is " + dx); //should be 3.0

System.out.println("dy is " + dy); //should be 4.0

return 0.0;

}

//next step to square distances

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); //should get 25.0

return 0.0;

}

//finally sqrt to get answer and return result

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;

}

//METHOD COMPOSITION

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));

}

}