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‎Chapter_06/samples/GreatestCommonDivisorMethod.java

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package chapter_six.samples;
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import java.util.Scanner;
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/** Listing 6.6 GreatestCommonDivisorMethod.java */
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public class GreatestCommonDivisorMethod
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{
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/** Main method */
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public static void main(String[] args)
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{
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// Create a Scanner
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Scanner input = new Scanner(System.in);
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// Prompt the user to enter two integers
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System.out.print("Enter first integer: ");
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int n1 = input.nextInt();
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System.out.print("Enter second integer: ");
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int n2 = input.nextInt();
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System.out.println("The greatest common divisor for " + n1 +
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" and " + n2 + " is " + gcd(n1, n2));
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}
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/** Return the gcd of two integers */
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public static int gcd(int n1,int n2)
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{
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int gcd = 1; // Initial gcd is 1
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int k = 2; // Possible gcd
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while (k <= n1 && k <= n2)
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{
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if (n1 % k == 0 && n2 % k == 0)
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gcd = k; // Update gcd
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k++;
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}
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return gcd; // Return gcd
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}
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}

‎Chapter_06/samples/Hex2Dec.java

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package chapter_six.samples;
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import java.util.Scanner;
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/** Listing 6.8 Hex2Dec.java */
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public class Hex2Dec
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{
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/** Main method */
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public static void main(String[] args)
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{
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// Create a Scanner
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Scanner input = new Scanner(System.in);
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// Prompt the user to enter a string
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System.out.print("Enter a hex number: ");
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String hex = input.nextLine();
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System.out.println("The decimal value for hex number "
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+ hex + " is " + hexToDecimal(hex.toUpperCase()));
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}
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public static int hexToDecimal(String hex)
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{
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int decimalValue = 0;
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for (int i = 0; i < hex.length(); i++)
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{
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char hexChar = hex.charAt(i);
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decimalValue = decimalValue * 16 + hexCharToDecimal(hexChar);
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}
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return decimalValue;
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}
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public static int hexCharToDecimal(char ch)
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{
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if (ch >= 'A' && ch <= 'F')
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return 10 + ch - 'A';
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else // ch is '0', '1', ..., or '9'
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return ch - '0';
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}
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}

‎Chapter_06/samples/Increment.java

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package chapter_six.samples;
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/** Listing 6.4 Increment.java */
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public class Increment
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{
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public static void main(String[] args)
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{
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int x = 1;
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System.out.println("Before the call, x is " + x);
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increment(x);
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System.out.println("After the call, x is " + x);
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}
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public static void increment(int n)
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{
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n++;
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System.out.println("n inside the method is " + n);
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}
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}

‎Chapter_06/samples/PrimeNumberMethod.java

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package chapter_six.samples;
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/** Listing 6.7 PrimeNumberMethod.java */
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public class PrimeNumberMethod
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{
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public static void main(String[] args)
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{
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System.out.println("The first 50 prime numbers are \n");
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printPrimeNumbers(50);
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}
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public static void printPrimeNumbers(int numberOfPrimes)
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{
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final int NUMBER_OF_PRIMES_PER_LINE = 10; // Display 10 per line
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int count = 0; // Count the number of prime numbers
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int number = 2; // A number to be tested for primeness
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// Repeatedly find prime numbers
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while (count < numberOfPrimes)
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{
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// Print the prime number and increase the count
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if (isPrime(number))
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{
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count++; // Increase the count
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if (count % NUMBER_OF_PRIMES_PER_LINE == 0)
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// Print the number and advance to the new line
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System.out.printf("%−5d\n", number);
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else
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System.out.printf("%−5d", number);
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}
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// Check whether the next number is prime
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number++;
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}
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}
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/** Check whether number is prime */
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public static boolean isPrime(int number)
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{
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for (int divisor = 2; divisor <= number / 2; divisor++)
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{
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if (number % divisor == 0) // If true, number is not prime
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return false; // Number is not a prime
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}
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return true;
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}
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}

‎Chapter_06/samples/PrintCalendar.java

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package chapter_six.samples;
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import java.util.Scanner;
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/**
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* Listing 6.12 PrintCalendar.java
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*/
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public class PrintCalendar {
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/**
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* Main method
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*/
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public static void main(String[] args)
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{
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Scanner input = new Scanner(System.in);
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// Prompt the user to enter year
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System.out.print("Enter full year (e.g., 2012): ");
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int year = input.nextInt();
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// Prompt the user to enter month
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System.out.print("Enter month as a number between 1 and 12: ");
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int month = input.nextInt();
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// Print calendar for the month of the year
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printMonth(year, month);
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}
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/**
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* Print the calendar for a month in a year
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*/
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public static void printMonth(int year, int month)
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{
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// Print the headings of the calendar
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printMonthTitle(year, month);
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// Print the body of the calendar
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printMonthBody(year, month);
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}
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/**
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* Print the month title, e.g., March 2012
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*/
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public static void printMonthTitle(int year, int month)
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{
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System.out.println(" " + getMonthName(month)
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+ " " + year);
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System.out.println("−−−−−−−−−−−−−−−−−−−−−−−−−−−−−");
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System.out.println(" Sun Mon Tue Wed Thu Fri Sat");
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}
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/**
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* Get the English name for the month
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*/
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public static String getMonthName(int month)
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{
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String monthName = "";
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switch (month)
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{
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case 1:
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monthName = "January";
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break;
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case 2:
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monthName = "February";
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break;
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case 3:
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monthName = "March";
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break;
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case 4:
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monthName = "April";
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break;
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case 5:
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monthName = "May";
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break;
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case 6:
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monthName = "June";
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break;
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case 7:
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monthName = "July";
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break;
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case 8:
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monthName = "August";
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break;
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case 9:
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monthName = "September";
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break;
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case 10:
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monthName = "October";
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break;
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case 11:
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monthName = "November";
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break;
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case 12:
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monthName = "December";
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}
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return monthName;
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}
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/**
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* Print month body
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*/
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public static void printMonthBody(int year, int month)
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{
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// Get start day of the week for the first date in the month
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int startDay = getStartDay(year, month);
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// Get number of days in the month
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int numberOfDaysInMonth = getNumberOfDaysInMonth(year, month);
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// Pad space before the first day of the month
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int i = 0;
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for (i = 0; i < startDay; i++)
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System.out.print(" ");
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for (i = 1; i <= numberOfDaysInMonth; i++)
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{
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System.out.printf("%4d", i);
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if ((i + startDay) % 7 == 0)
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System.out.println();
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}
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System.out.println();
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}
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/**
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* Get the start day of month/1/year
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*/
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public static int getStartDay(int year, int month)
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{
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final int START_DAY_FOR_JAN_1_1800 = 3;
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// Get total number of days from 1/1/1800 to month/1/year
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int totalNumberOfDays = getTotalNumberOfDays(year, month);
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// Return the start day for month/1/year
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return (totalNumberOfDays + START_DAY_FOR_JAN_1_1800) % 7;
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}
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/**
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* Get the total number of days since January 1, 1800
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*/
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public static int getTotalNumberOfDays(int year, int month)
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{
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int total = 0;
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// Get the total days from 1800 to 1/1/year
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for (int i = 1800; i < year; i++)
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if (isLeapYear(i))
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total = total + 366;
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else
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total = total + 365;
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// Add days from Jan to the month prior to the calendar month
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for (int i = 1; i < month; i++)
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total = total + getNumberOfDaysInMonth(year, i);
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return total;
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}
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/**
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* Get the number of days in a month
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*/
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public static int getNumberOfDaysInMonth(int year, int month)
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{
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if (month == 1 || month == 3 || month == 5 || month == 7 ||
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month == 8 || month == 10 || month == 12)
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return 31;
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if (month == 4 || month == 6 || month == 9 || month == 11)
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return 30;
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if (month == 2) return isLeapYear(year) ? 29 : 28;
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return 0; // If month is incorrect
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}
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/**
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* Determine if it is a leap year
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*/
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public static boolean isLeapYear(int year)
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{
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return year % 400 == 0 || (year % 4 == 0 && year % 100 != 0);
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}
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}

‎Chapter_06/samples/RandomCharacter.java

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package chapter_six.samples;
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/**
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* Listing 6.10 RandomCharacter.java
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*/
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public class RandomCharacter
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{
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/**
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* Generate a random character between ch1 and ch2
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*/
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public static char getRandomCharacter(char ch1, char ch2)
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{
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return (char) (ch1 + Math.random() * (ch2 - ch1 + 1));
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}
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/**
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* Generate a random lowercase letter
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*/
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public static char getRandomLowerCaseLetter()
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{
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return getRandomCharacter('a', 'z');
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}
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/**
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* Generate a random uppercase letter
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*/
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public static char getRandomUpperCaseLetter()
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{
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return getRandomCharacter('A', 'Z');
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}
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/**
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* Generate a random digit character
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*/
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public static char getRandomDigitCharacter()
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{
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return getRandomCharacter('0', '9');
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}
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/**
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* Generate a random character
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*/
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public static char getRandomCharacter()
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{
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return getRandomCharacter('\u0000', '\uFFFF');
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}
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}

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