Example 6

Chapter 6

//--------


Introduction to Java Programming, Tenth Edition, Y. Daniel Liang

public class TestMax {
  /** Main method */
  public static void main(String[] args) {
    int i = 5;
    int j = 2;
    int k = max(i, j);
    System.out.println("The maximum between " + i +
      " and " + j + " is " + k);
  }

  /** Return the max between two numbers */
  public static int max(int num1, int num2) {
    int result;

    if (num1 > num2)
      result = num1;
    else
      result = num2;

    return result;
  }
}

//----------


Introduction to Java Programming, Tenth Edition, Y. Daniel Liang

public class TestVoidMethod {
  public static void main(String[] args) {
    System.out.print("The grade is ");
    printGrade(78.5);

    System.out.print("The grade is ");
    printGrade(59.5);
  }

  public static void printGrade(double score) {
    if (score >= 90.0) {
      System.out.println('A');
    }
    else if (score >= 80.0) {
      System.out.println('B');
    }
    else if (score >= 70.0) {
      System.out.println('C');
    }
    else if (score >= 60.0) {
      System.out.println('D');
    }
    else {
      System.out.println('F');
    }
  }
}

//------------


Introduction to Java Programming, Tenth Edition, Y. Daniel Liang

public class TestReturnGradeMethod {
  public static void main(String[] args) {
    System.out.print("The grade is " + getGrade(78.5));
    System.out.print("\nThe grade is " + getGrade(59.5));
  }

  public static char getGrade(double score) {
    if (score >= 90.0)
      return 'A';
    else if (score >= 80.0)
      return 'B';
    else if (score >= 70.0)
      return 'C';
    else if (score >= 60.0)
      return 'D';
    else
      return 'F';
  }
}

//------------


Introduction to Java Programming, Tenth Edition, Y. Daniel Liang

public class Increment {
  public static void main(String[] args) {
    int x = 1;
    System.out.println("Before the call, x is " + x);
    increment(x);
    System.out.println("after the call, x is " + x);
  }

  public static void increment(int n) {
    n++;
    System.out.println("n inside the method is " + n);
  }
}

//-----------


Introduction to Java Programming, Tenth Edition, Y. Daniel Liang

public class TestPassByValue {
  /** Main method */
  public static void main(String[] args) {
    // Declare and initialize variables
    int num1 = 1;
    int num2 = 2;

    System.out.println("Before invoking the swap method, num1 is " +
      num1 + " and num2 is " + num2);

    // Invoke the swap method to attempt to swap two variables
    swap(num1, num2);

    System.out.println("After invoking the swap method, num1 is " +
      num1 + " and num2 is " + num2);
  }

  /** Swap two variables */
  public static void swap(int n1, int n2) {
    System.out.println("\tInside the swap method");
    System.out.println("\t\tBefore swapping, n1 is " + n1
      + " and n2 is " + n2);

    // Swap n1 with n2
    int temp = n1;
    n1 = n2;
    n2 = temp;

    System.out.println("\t\tAfter swapping, n1 is " + n1
      + " and n2 is " + n2);
  }
}

//-----------


Introduction to Java Programming, Tenth Edition, Y. Daniel Liang

import java.util.Scanner;

public class GreatestCommonDivisorMethod {
  /** Main method */
  public static void main(String[] args) {
    // Create a Scanner
    Scanner input = new Scanner(System.in);

    // Prompt the user to enter two integers
    System.out.print("Enter first integer: ");
    int n1 = input.nextInt();
    System.out.print("Enter second integer: ");
    int n2 = input.nextInt();

    System.out.println("The greatest common divisor for " + n1 +
      " and " + n2 + " is " + gcd(n1, n2));
  }

  /** Return the gcd of two integers */
  public static int gcd(int n1, int n2) {
    int gcd = 1; // Initial gcd is 1
    int k = 1; // Possible gcd
   
    while (k <= n1 && k <= n2) {
      if (n1 % k == 0 && n2 % k == 0)
        gcd = k; // Update gcd
      k++;
    }

    return gcd; // Return gcd
  }
}

//--------------


Introduction to Java Programming, Tenth Edition, Y. Daniel Liang

public class PrimeNumberMethod {
  public static void main(String[] args) {
    System.out.println("The first 50 prime numbers are \n");
    printPrimeNumbers(50);
  }

  public static void printPrimeNumbers(int numberOfPrimes) {
    final int NUMBER_OF_PRIMES_PER_LINE = 10; // Display 10 per line
    int count = 0; // Count the number of prime numbers
    int number = 2; // A number to be tested for primeness

    // Repeatedly find prime numbers
    while (count < numberOfPrimes) {
      // Print the prime number and increase the count
      if (isPrime(number)) {
        count++; // Increase the count

        if (count % NUMBER_OF_PRIMES_PER_LINE == 0) {
          // Print the number and advance to the new line
          System.out.printf("%-5s\n", number);
        }
        else
          System.out.printf("%-5s", number);
      }

      // Check if the next number is prime
      number++;
    }
  }

  /** Check whether number is prime */
  public static boolean isPrime(int number) {
    for (int divisor = 2; divisor <= number / 2; divisor++) {
      if (number % divisor == 0) { // If true, number is not prime
        return false; // number is not a prime
      }
    }

    return true; // number is prime
  }
}

//------------


Introduction to Java Programming, Tenth Edition, Y. Daniel Liang

import java.util.Scanner;

public class Hex2Dec {
  /** Main method */
  public static void main(String[] args) {
    // Create a Scanner
    Scanner input = new Scanner(System.in);

    // Prompt the user to enter a string
    System.out.print("Enter a hex number: ");
    String hex = input.nextLine();

    System.out.println("The decimal value for hex number "
      + hex + " is " + hexToDecimal(hex.toUpperCase()));
  }

  public static int hexToDecimal(String hex) {
    int decimalValue = 0;
    for (int i = 0; i < hex.length(); i++) {
      char hexChar = hex.charAt(i);
      decimalValue = decimalValue * 16 + hexCharToDecimal(hexChar);
    }
   
    return decimalValue;
  }

  public static int hexCharToDecimal(char ch) {
    if (ch >= 'A' && ch <= 'F')
      return 10 + ch - 'A';
    else // ch is '0', '1', ..., or '9'
      return ch - '0';
  }
}

//---------------


Introduction to Java Programming, Tenth Edition, Y. Daniel Liang

public class TestMethodOverloading {
  /** Main method */
  public static void main(String[] args) {
    // Invoke the max method with int parameters
    System.out.println("The maximum of 3 and 4 is "
      + max(3, 4));

    // Invoke the max method with the double parameters
    System.out.println("The maximum of 3.0 and 5.4 is "
      + max(3.0, 5.4));

    // Invoke the max method with three double parameters
    System.out.println("The maximum of 3.0, 5.4, and 10.14 is "
      + max(3.0, 5.4, 10.14));
  }

  /** Return the max of two int values */
  public static int max(int num1, int num2) {
    if (num1 > num2)
      return num1;
    else
      return num2;
  }

  /** Find the max of two double values */
  public static double max(double num1, double num2) {
    if (num1 > num2)
      return num1;
    else
      return num2;
  }

  /** Return the max of three double values */
  public static double max(double num1, double num2, double num3) {
    return max(max(num1, num2), num3);
  }
}

//---------------


Introduction to Java Programming, Tenth Edition, Y. Daniel Liang

public class RandomCharacter {
  /** Generate a random character between ch1 and ch2 */
  public static char getRandomCharacter(char ch1, char ch2) {
    return (char)(ch1 + Math.random() * (ch2 - ch1 + 1));
  }

  /** Generate a random lowercase letter */
  public static char getRandomLowerCaseLetter() {
    return getRandomCharacter('a', 'z');
  }

  /** Generate a random uppercase letter */
  public static char getRandomUpperCaseLetter() {
    return getRandomCharacter('A', 'Z');
  }

  /** Generate a random digit character */
  public static char getRandomDigitCharacter() {
    return getRandomCharacter('0', '9');
  }

  /** Generate a random character */
  public static char getRandomCharacter() {
    return getRandomCharacter('\u0000', '\uFFFF');
  }
}

//-----------


Introduction to Java Programming, Tenth Edition, Y. Daniel Liang

public class TestRandomCharacter {
  /** Main method */
  public static void main(String args[]) {
    final int NUMBER_OF_CHARS = 175;
    final int CHARS_PER_LINE = 25;

    // Print random characters between 'a' and 'z', 25 chars per line
    for (int i = 0; i < NUMBER_OF_CHARS; i++) {
      char ch = RandomCharacter.getRandomLowerCaseLetter();
      if ((i + 1) % CHARS_PER_LINE == 0)
        System.out.println(ch);
      else
        System.out.print(ch);
    }
  }
}

//-----------


Introduction to Java Programming, Tenth Edition, Y. Daniel Liang

import java.util.Scanner;

public class PrintCalendar {
  /** Main method */
  public static void main(String[] args) {
    Scanner input = new Scanner(System.in);

    // Prompt the user to enter year
    System.out.print("Enter full year (e.g., 2001): ");
    int year = input.nextInt();

    // Prompt the user to enter month
    System.out.print("Enter month in number between 1 and 12: ");
    int month = input.nextInt();

    // Print calendar for the month of the year
    printMonth(year, month);
  }

  /** Print the calendar for a month in a year */
  public static void printMonth(int year, int month) {
    // Print the headings of the calendar
    printMonthTitle(year, month);

    // Print the body of the calendar
    printMonthBody(year, month);
  }

  /** Print the month title, e.g., May, 1999 */
  public static void printMonthTitle(int year, int month) {
    System.out.println("         " + getMonthName(month)
      + " " + year);
    System.out.println("-----------------------------");
    System.out.println(" Sun Mon Tue Wed Thu Fri Sat");
  }

  /** Get the English name for the month */
  public static String getMonthName(int month) {
    String monthName = "";
    switch (month) {
      case 1: monthName = "January"; break;
      case 2: monthName = "February"; break;
      case 3: monthName = "March"; break;
      case 4: monthName = "April"; break;
      case 5: monthName = "May"; break;
      case 6: monthName = "June"; break;
      case 7: monthName = "July"; break;
      case 8: monthName = "August"; break;
      case 9: monthName = "September"; break;
      case 10: monthName = "October"; break;
      case 11: monthName = "November"; break;
      case 12: monthName = "December";
    }

    return monthName;
  }

  /** Print month body */
  public static void printMonthBody(int year, int month) {
    // Get start day of the week for the first date in the month
    int startDay = getStartDay(year, month);

    // Get number of days in the month
    int numberOfDaysInMonth = getNumberOfDaysInMonth(year, month);

    // Pad space before the first day of the month
    int i = 0;
    for (i = 0; i < startDay; i++)
      System.out.print("    ");

    for (i = 1; i <= numberOfDaysInMonth; i++) {
      System.out.printf("%4d", i);

      if ((i + startDay) % 7 == 0)
        System.out.println();
    }

    System.out.println();
  }

  /** Get the start day of month/1/year */
  public static int getStartDay(int year, int month) {
    final int START_DAY_FOR_JAN_1_1800 = 3;
    // Get total number of days from 1/1/1800 to month/1/year
    int totalNumberOfDays = getTotalNumberOfDays(year, month);

    // Return the start day for month/1/year
    return (totalNumberOfDays + START_DAY_FOR_JAN_1_1800) % 7;
  }

  /** Get the total number of days since January 1, 1800 */
  public static int getTotalNumberOfDays(int year, int month) {
    int total = 0;

    // Get the total days from 1800 to 1/1/year
    for (int i = 1800; i < year; i++)
      if (isLeapYear(i))
        total = total + 366;
      else
        total = total + 365;

    // Add days from Jan to the month prior to the calendar month
    for (int i = 1; i < month; i++)
      total = total + getNumberOfDaysInMonth(year, i);

    return total;
  }

  /** Get the number of days in a month */
  public static int getNumberOfDaysInMonth(int year, int month) {
    if (month == 1 || month == 3 || month == 5 || month == 7 ||
      month == 8 || month == 10 || month == 12)
      return 31;

    if (month == 4 || month == 6 || month == 9 || month == 11)
      return 30;

    if (month == 2) return isLeapYear(year) ? 29 : 28;

    return 0; // If month is incorrect
  }

  /** Determine if it is a leap year */
  public static boolean isLeapYear(int year) {
    return year % 400 == 0 || (year % 4 == 0 && year % 100 != 0);
  }
}

//----------