erwise noted in the question, assume that parameters in method calls are not null and that methods are called only when their preconditions are satisfied. In writing solutions for each question, you may use any of the accessible methods that are listed in classes defined in that question. Writing significant amounts of code that can be replaced by a call to one of these methods will not receive full credit. This question involves the use of check digits, which can be used to help detect if an error has occurred when a number is entered or transmitted electronically. An algorithm for computing a check digit, based on the digits of a number, is provided in part (a). The CheckDigit class is shown below. You will write two methods of the CheckDigit class. public class CheckDigit { /** Returns the check digit for num, as described in part (a).
SHOW ALL YOUR WORK. REMEMBER THAT PROGRAM SEGMENTS ARE TO BE WRITTEN IN JAVA.
- Assume that the classes listed in the Java Quick Reference have been imported where appropriate.
- Unless otherwise noted in the question, assume that parameters in method calls are not null and that methods are called only when their preconditions are satisfied.
- In writing solutions for each question, you may use any of the accessible methods that are listed in classes defined in that question. Writing significant amounts of code that can be replaced by a call to one of these methods will not receive full credit.
This question involves the use of check digits, which can be used to help detect if an error has occurred when a number is entered or transmitted electronically. An
The CheckDigit class is shown below. You will write two methods of the CheckDigit class.
public class CheckDigit
{
/** Returns the check digit for num, as described in part (a).
* Precondition: The number of digits in num is between one and six, inclusive.
* num >= 0
*/
public static int getCheck(int num)
{
/* to be implemented in part (a) */
}
/** Returns true if numWithCheckDigit is valid, or false otherwise, as described in part (b).
* Precondition: The number of digits in numWithCheckDigit is between two and seven, inclusive.
* numWithCheckDigit >= 0
*/
public static boolean isValid(int numWithCheckDigit)
{
/* to be implemented in part (b) */
}
/** Returns the number of digits in num. */
public static int getNumberOfDigits(int num)
{
/* implementation not shown */
}
/** Returns the nth digit of num.
* Precondition: n >= 1 and n <= the number of digits in num
*/
public static int getDigit(int num, int n)
{
/* implementation not shown */
}
// There may be instance variables, constructors, and methods not shown.
}
(a) Write the getCheck method, which computes the check digit for a number according to the following rules.
- Multiply the first digit by 7, the second digit (if one exists) by 6, the third digit (if one exists) by 5, and so on. The length of the method's int parameter is at most six; therefore, the last digit of a six-digit number will be multiplied by 2.
- Add the products calculated in the previous step.
- Extract the check digit, which is the rightmost digit of the sum calculated in the previous step.
The following are examples of the check-digit calculation.
Example 1, where num has the value 283415
- The sum to calculate is (2x7)+(8x6)+(3x5)+(4x4)+(1x3)+(5x2)=14+48+15+16+3+10=106.
- The check digit is the rightmost digit of 106, or 6, and getCheck returns the integer value 6.
Example 2, where num has the value 2183
- The sum to calculate is (2x7)+(1x6)+(8x5)+(3x4)=14+6+40+12=72.
- The check digit is the rightmost digit of 72, or 2, and getCheck returns the integer value 2.
Two helper methods, getNumberOfDigits and getDigit, have been provided.
- getNumberOfDigits returns the number of digits in its int parameter.
- getDigit returns the nth digit of its int parameter.
The following are examples of the use of getNumberOfDigits and getDigit.
| Method Call | Return Value | Explanation |
| getNumberOfDigits(283415) | 6 | The number 283415 has 6 digits. |
| getDigit(283415, 1) | 2 | The first digit of 283415 is 2. |
| getDigit(283415, 5) | 1 | The fifth digit of 283415 is 1. |
Complete the getCheck method below. You must use getNumberOfDigits and getDigit appropriately to receive full credit.
/** Returns the check digit for num, as described in part (a).
* Precondition: The number of digits in num is between one and six, inclusive.
* num >= 0
*/
public static int getCheck(int num)
==============================================
(b) Write the isValid method. The method returns true if its parameter numWithCheckDigit, which represents a number containing a check digit, is valid, and false otherwise. The check digit is always the rightmost digit of numWithCheckDigit.
The following table shows some examples of the use of isValid.
| Method Call | Return Value | Explanation |
| getCheck(159) | 2 | The check digit for 159 is 2. |
| isValid(1592) | true | The number 1592 is a valid combination of a number (159) and its check digit (2). |
| isValid(1593) | false | The number 1593 is not a valid combination of a number (159) and its check digit (3) because 2 is the check digit for 159. |
Complete method isValid below. Assume that getCheck works as specified, regardless of what you wrote in part (a). You must use getCheck appropriately to receive full credit.
/** Returns true if numWithCheckDigit is valid, or false otherwise, as described in part (b).
* Precondition: The number of digits in numWithCheckDigit is between two and seven, inclusive.
* numWithCheckDigit >= 0
*/
public static boolean isValid(int numWithCheckDigit)
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