Add Credit Card project

Author: phrdang

src/com/codefortomorrow/intermediate/chapter11/practice/CreditCard.java

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+package com.codefortomorrow.intermediate.chapter11.practice;
+
+/*
+Credit card numbers follow certain patterns. A credit card number
+must have between 13 and 16 digits. It must start with:
+■ 4 for Visa cards
+■ 5 for Master cards
+■ 37 for American Express cards
+■ 6 for Discover cards
+
+In 1954, Hans Luhn of IBM proposed an algorithm for validating credit card
+numbers. The algorithm is useful to determine whether a card number is entered
+correctly or whether a credit card is scanned correctly by a scanner. Credit card
+numbers are generated following this validity check, commonly known as the
+Luhn check or the Mod 10 check, which can be described as follows
+(for illustration, consider the card number 4388576018402626):
+
+1. Double every second digit from right to left. If doubling of a digit results in a
+two-digit number, add up the two digits to get a single-digit number.
+4388576018402626
+2 * 2 = 4
+2 * 2 = 4
+4 * 2 = 8
+1 * 2 = 2
+6 * 2 = 12 (1 + 2 = 3)
+5 * 2 = 10 (1 + 0 = 1)
+8 * 2 = 16 (1 + 6 = 7)
+4 * 2 = 8
+
+2. Now add all single-digit numbers from Step 1.
+4 + 4 + 8 + 2 + 3 + 1 + 7 + 8 = 37
+
+3. Add all digits in the odd places from right to left in the card number.
+6 + 6 + 0 + 8 + 0 + 7 + 8 + 3 = 38
+
+4. Sum the results from Step 2 and Step 3.
+37 + 38 = 75
+
+5. If the result from Step 4 is divisible by 10, the card number is valid; otherwise,
+it is invalid. For example, the number 4388576018402626 is invalid, but the
+number 4388576018410707 is valid.
+
+Write a program that prompts the user to enter a credit card number as a long
+integer. Display whether the number is valid or invalid. Design your program to
+use the following methods:
+
+Returns true if the card number is valid
+public static boolean isValid(long number)
+
+Gets the result from Step 2
+public static int sumOfDoubleEvenPlace(long number)
+
+Returns this number if it is a single digit, otherwise,
+return the sum of the two digits
+public static int getDigit(int number)
+
+Returns sum of odd-place digits in number
+public static int sumOfOddPlace(long number)
+
+Returns true if the digit d is a prefix for number
+public static boolean prefixMatched(long number, int d)
+
+Returns the number of digits in d
+public static int getSize(long d)
+
+Returns the first k number of digits from number. If the
+number of digits in number is less than k, return number.
+public static long getPrefix(long number, int k)
+
+Here are sample runs of the program:
+
+Enter a credit card number: 4388576018410707
+4388576018410707 is valid
+
+Enter a credit card number: 4388576018402626
+4388576018402626 is invalid
+
+Bonus points if you can also print to the user
+what type of card the number is, and for writing JavaDoc comments.
+
+Note: If you need more card numbers to test, you can look here:
+https://www.simplify.com/commerce/docs/testing/test-card-numbers
+(or simply search "test credit card numbers" on Google).
+
+Note: The practice template has method stubs written for you.
+Simply delete the default return values and start coding!
+
+Adapted from Exercise 6.31, Introduction to Java Programming (Comprehensive),
+10th ed. by Y. Daniel Liang
+*/
+
+public class CreditCard {
+    public static void main(String[] args) {
+        // write code here
+    }
+	
+	/** Returns true if the card number is valid */
+	public static boolean isValid(long number) {
+		return false;
+	}
+	
+	/** Returns the sum of the doubled even-place digits, from right to left */
+	public static int sumOfDoubleEvenPlace(long number) {
+		return 0;
+	}
+	
+	/** 
+	 * Returns the given number if it is a single digit,
+	 * otherwise return the sum of the two digits
+	 */
+	public static int getDigit(int n) {				
+		return 0;		
+	}
+	
+	/** Returns the sum of the odd-place digits, from right to left */
+	public static int sumOfOddPlace(long number) {
+		return 0;
+	}
+
+	/** Return true if d is a prefix for a number */
+	public static boolean prefixMatched(long number, int d) {
+		return false;
+	}
+	
+	/** Returns the number of digits in the given number */
+	public static int getSize(long number) {
+		return 0;
+	}
+	
+	/** 
+	 * Returns the first k number of digits from number.
+	 * If the number of digits in number is less than k, 
+	 * returns number.
+	 */
+	public static long getPrefix(long number, int k) {
+		return 0;
+	}
+}