Java program to calculate the area of a circle : Console « Development Class « Java





Java program to calculate the area of a circle

Java program to calculate the area of a circle
  
/*
Java Programming for Engineers
Julio Sanchez
Maria P. Canton


ISBN: 0849308100
Publisher: CRC Press
*/

// File name: Area.java
//Reference: Chapter 5
//
//Java program to calculate the area of a circle
//Topics:
// 1. Using numeric variables and constants
// 2. Obtaining keyboard input
// 3. Displaying program data
// 4. Performing simple numeric calculations
//
//Requires:
// 1. Keyin class in the current directory

public class Area {
  // Constant PI is defined at the class level
  static final double PI = 3.141592653589793;

  public static void main(String[] args) {
    // Local variables
    double radius, area;

    // Input radius from keyboard
    radius = Keyin.inDouble("Enter radius: ");

    // Perform calculations and display result
    area = PI * (radius * radius);
    System.out.println("The area is: " + area);
  }
}

//**********************************************************
//**********************************************************
//Program: Keyin
//Reference: Session 20
//Topics:
//   1. Using the read() method of the ImputStream class
//      in the java.io package
//   2. Developing a class for performing basic console
//      input of character and numeric types
//**********************************************************
//**********************************************************

class Keyin {

  //*******************************
  //   support methods
  //*******************************
  //Method to display the user's prompt string
  public static void printPrompt(String prompt) {
    System.out.print(prompt + " ");
    System.out.flush();
  }

  //Method to make sure no data is available in the
  //input stream
  public static void inputFlush() {
    int dummy;
    int bAvail;

    try {
      while ((System.in.available()) != 0)
        dummy = System.in.read();
    } catch (java.io.IOException e) {
      System.out.println("Input error");
    }
  }

  //********************************
  //  data input methods for
  //string, int, char, and double
  //********************************
  public static String inString(String prompt) {
    inputFlush();
    printPrompt(prompt);
    return inString();
  }

  public static String inString() {
    int aChar;
    String s = "";
    boolean finished = false;

    while (!finished) {
      try {
        aChar = System.in.read();
        if (aChar < 0 || (char) aChar == '\n')
          finished = true;
        else if ((char) aChar != '\r')
          s = s + (char) aChar; // Enter into string
      }

      catch (java.io.IOException e) {
        System.out.println("Input error");
        finished = true;
      }
    }
    return s;
  }

  public static int inInt(String prompt) {
    while (true) {
      inputFlush();
      printPrompt(prompt);
      try {
        return Integer.valueOf(inString().trim()).intValue();
      }

      catch (NumberFormatException e) {
        System.out.println("Invalid input. Not an integer");
      }
    }
  }

  public static char inChar(String prompt) {
    int aChar = 0;

    inputFlush();
    printPrompt(prompt);

    try {
      aChar = System.in.read();
    }

    catch (java.io.IOException e) {
      System.out.println("Input error");
    }
    inputFlush();
    return (char) aChar;
  }

  public static double inDouble(String prompt) {
    while (true) {
      inputFlush();
      printPrompt(prompt);
      try {
        return Double.valueOf(inString().trim()).doubleValue();
      }

      catch (NumberFormatException e) {
        System.out
            .println("Invalid input. Not a floating point number");
      }
    }
  }
}

           
         
    
  










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