To encrypt a letter pair, the rectangle formed by the two letters is used. Each letter of the original pair is replaced by the letter located on the same row and in the other corner of the rectangle. If both letters happen to be in the same row or colum, the letters are swapped..
For example, in the following arrangement AP is encrypted as DM.
S T U V W X
Y Z 0 1 2 3
4 5 6 7 8 9
A---B---C---D E F
| |
G H I J K L
| |
M---N---O---P Q R
Consider the following declration for a class that
uses this scheme to encrypt a word (see
also Point.java) only
the method/constructors headers are shown, not the bodies.
public class Point
{
/**
* Construct a point with given row/column
*/
public Point(int row, int col)
{
// not shown
}
/**
* return the row of this point
*/
public int getRow()
{
// not shown
}
/**
* return the column of this point
*/
public int getColumn()
{
// not shown
}
}
The class Encryptor is partially shown below.
public class Encryptor
{
/**
* Initialize an Encryptor so that EncryptWord works
*/
public Encryptor()
{
// not shown
}
/**
* convert a string to an encrypted form
* @param word is encrypted
* @return an encrypted form of word
*/
public String encryptWord(String word)
{
// not shown
}
/**
* encrypt a two-character string
* @precondition pair has two characters
* @param pair is the string encrypted
* @return an encrypted form of pair
*/
private String encryptTwo(String pair)
{
// not shown
}
/**
* find/return a pair for the single character string ch
* @precondition ch.length() == 1; ch is a single character string
* @return the coordinates of ch in the encryption matrix
*/
private Point getCoordinates(String ch)
{
// not shown
}
private String myMatrix[][];
}
Write member function getCoordinates, as started below. getCoordinates takes a single character string representing a capital letter or a digit and returns its row and column in the 2-dimensional array myMatrix.
The following example shows the point locations of the String ch in the given matrix.
| myMatrix | ch | Point coordinates |
|---|---|---|
S T U V W X Y Z 0 1 2 3 4 5 6 7 8 9 A B C D E F G H I J K L M N O P Q R |
p 8 M |
row = 5 col = 3 row = 2 col = 4 row = 5 col = 0 |
Complete method getCoordinates below.
/**
* find/return a pair for the single character string ch
* precondition: ch is a single character string with
* "A" <= ch <= "Z" or "0" <= ch <= "9"
* @return the coordinates of ch in the encryption matrix
*/
private Point getCoordinates(String ch)
The encoding of a letter pair is formed as follows.
For example, to encrypt the string "NE", look at the rectangle with corners "N" and "E". The encrypted letter pair is "QB" because "Q" is the letter at the other corner on the same row as "N", and "B" is the letter at the other corner on the same row as "E".
S T U V W X
Y Z 0 1 2 3
4 5 6 7 8 9
A B---C---D---E F
| |
G H I J K L
| |
M N---O---P---Q R
| Letters: | "BR" | "NE" | "ET" | "RE" | "TH" | "PR" | "GG" |
| Encrypted: | "FN" | "QB" | "BW" | "QF" | "HT" | "RP" | "GG" |
In writing encryptTwo you may call getCoordinates specified in part (a). Assume that getCoordinates works as specified, regardless of what you wrote in part (a).
Complete method encryptTwo below.
/**
* encrypt a two-character string
* @precondition pair.length() == 2; pair has two characters
* @param pair is the string encrypted
* @return an encrypted form of pair
*/
private String encryptTwo(String pair)
The following are examples of encrypted words using the 2-dimensional array shown below.
S T U V W X Y Z 0 1 2 3 4 5 6 7 8 9 A B C D E F G H I J K L M N O P Q R
| Word: | "COMPUTER" | "SCIENCE" | "STUDENTS" |
| Encrypted: | "OCPMTUFQ" | "UAKCOBE" | "TSVCBQST" |
In writing encryptWord you may call encryptTwo specified in part (b). Assume that encryptTwo works as specified, regardless of what you wrote in part (b).
/**
* Converts a string to an encrypted form.
* @precondition: word contains only letters A-Z or
* digits 0-9
* @param word to be encrypted
* @return the encrypted form of word
*/
public String encryptWord(String word)
answer
Encryptor.java and html-form of .java file