Java Program Methods

Java Program for Eclipse

Lab Objectives: To develop ability to write void and value returning methods and to call them

Introduction: Methods are commonly used to break a problem down into small manageable pieces. A large task can be broken down into smaller tasks (methods) that contain the details of how to complete that small task. The larger problem is then solved by implementing the smaller tasks (calling the methods) in the correct order.

This also allows for efficiencies, since the method can be called as many times as needed without rewriting the code each time.

Task #1 void Methods

1.   Type the code (Geometry.java) shown in at the end of this handout. This program will compile, but when you run it, it doesn’t appear to do anything except wait. That is because it is waiting for user input, but the user doesn’t have the menu to choose from yet. We will need to create this.

2.   Above the main method, but in the Geometry class, create a static method called printMenu that has no parameter list and does not return a value. It will simply print out instructions for the user with a menu of options for the user to choose from. The menu should appear to the user as:

This is a geometry calculator

Choose what you would like to calculate

1. Find the area of a circle

2. Find the area of a rectangle

3. Find the area of a triangle

4. Find the circumference of a circle

5. Find the perimeter of a rectangle

6. Find the perimeter of a triangle

Enter the number of your choice:

3.   Add a line in the main method that calls the printMenu method as indicated by the comments.

4.   Compile, debug, and run.  You should be able to choose any option, but you will always get 0 for the answer. We will fix this in the next task.

Task #2 Value-Returning Methods

1.   Write a static method called circleArea that takes in the radius of the circle and returns the area using the formula A = π r 2 .

2.   Write a static method called rectangleArea that takes in the length and width of

the rectangle and returns the area using the formula A = lw.

3.   Write a static method called triangleArea that takes in the base and height of the triangle and returns the area using the formula A = ½bh.

4.   Write a static method called circleCircumference that takes in the radius of the circle and returns the circumference using the formula C = 2πr.

5.   Write a static method called rectanglePerimeter that takes in the length and the width of the rectangle and returns the perimeter of the rectangle using the formula P = 2l +2w.

6.   Write a static method called trianglePerimeter that takes in the lengths of the three sides of the triangle and returns the perimeter of the triangle which is calculated by adding up the three sides.

Task #3 Calling Methods

1.   Add lines in the main method in the Geometry class which will call these methods. The comments indicate where to place the method calls.

2.   Compile, debug, and run.  Test out the program using your sample data.

import java.util.Scanner;
// Demonstration of static methods
public class PutYourClassHere
 {
 public static void main (String [] args)
  {
  int choice; //the user's choice
  double value = 0; //the value returned from the method
  char letter;  //the Y or N from the user's decision to exit 
  double radius; //the radius of the circle
  double length; //the length of the rectangle 
  double width,height;  //the width and height of the rectangle 
  double base;  //the base of the triangle 
  double side1,side2,side3;  // sides of the triangle

//create a scanner object to read from the keyboard
  Scanner keyboard = new Scanner (System.in);

//do loop was chose to allow the menu to be displayed first do
  do
  {
   //call the printMenu method here
   printMenu();
   choice = keyboard.nextInt();

  switch (choice)
  {
   case 1:
    System.out.print("Enter the radius of the circle:  ");
    radius = keyboard.nextDouble();
    value = circleArea(radius);
     //call the circleArea method and store the result in the value 
    System.out.println("The area of the circle is " + value);
    break;
   case 2:
    System.out.print("Enter the length of the rectangle:  "); 
    length = keyboard.nextDouble();
    System.out.print("Enter the width of the rectangle:  ");
    width = keyboard.nextDouble();
    value = rectangleArea(length,width);
    //call the rectangleArea method and store the result in the value 
    System.out.println("The area of the rectangle is " + value); 
    break;
   case 3:
    System.out.print("Enter the height of the triangle:  "); 
    height = keyboard.nextDouble(); 
    System.out.print("Enter the base of the triangle:  "); 
    base = keyboard.nextDouble();
    value = triangleArea(height,base);
    //call the triangleArea method and store the result in the value 
    System.out.println("The area of the triangle is " + value); 
    break;
   case 4:
    System.out.print("Enter the radius of the circle:  ");
    radius = keyboard.nextDouble();
    value = circleCircumference(radius);
    //call the circumference method and store the result in the value 
    System.out.println("The circumference of the circle is " + value); 
    break;
   case 5:
    System.out.print("Enter the length of the rectangle:  "); 
    length = keyboard.nextDouble(); 
    System.out.print("Enter the width of the rectangle:  "); 
    width = keyboard.nextDouble();
    value = rectanglePerimeter(length,width);
    //call the perimeter method and store the result in the value 
    System.out.println("The perimeter of the rectangle is " + value); 
    break;
   case 6:
    System.out.print("Enter the length of side 1 of the triangle:  ");
    side1 = keyboard.nextDouble();
    System.out.print("Enter the length of side 2 of the triangle:  ");
    side2 = keyboard.nextDouble();
    System.out.print("Enter the length of side 3 of the triangle:  ");
    side3 = keyboard.nextDouble();
    value = trianglePerimeter(side1,side2,side3);
    //call the perimeter method and store the result in the value 
    System.out.println("The perimeter of the triangle is " + value); 
    break;
   default:
  System.out.println("You did not enter a valid choice.");
     }//end of switch statement
//consumes the new line character after the number 
  keyboard.nextLine();

  System.out.println("Do you want to exit the program (Y/N)?:  "); 
  String answer = keyboard.nextLine();
  letter = answer.charAt(0); //select first character of response

  }while (letter != 'Y' && letter != 'y'); //end of do-while loop

 }//end of main

//insert your method definitions here
 public static void printMenu() {
  System.out.println("This is a geometry calculator ");
  System.out.println("Choose what you would like to calculate!");
  System.out.println("1. Find the area of a cirlce ");
  System.out.println("2. Find the area of a rectangle ");
  System.out.println("3. Find the area of a triangle ");
  System.out.println("4. Find the circumference of a cirle ");
  System.out.println("5. Find the perimeter of a rectangle ");
  System.out.println("6. Find the perimeter of a triangle");
  System.out.print("Enter the number of your choice: ");
 }
 public static double circleArea(double r) {
  return Math.PI * r * r;
 }
 public static double rectangleArea(double length, double width) {
  return length * width;
 }
 public static double triangleArea(double height, double base) {
  return .5 * height * base;
 }
 public static double circleCircumference(double r) {
  return 2 * Math.PI * r;
 }
 public static double rectanglePerimeter(double length,double width) {
  return 2 * length + 2 * width;
 }
 public static double trianglePerimeter(double side1,double side2, double side3) {
  return side1 + side2 + side3;
 }


}//end of class