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Java/ciphers/Caesar.java at dev · primary-code-test/Java · GitHub
primary-code-test
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ciphers
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Caesar.java
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package
ciphers
;
import
java
.
util
.
Scanner
;
/**
* A Java implementation of Caesar Cipher. /It is a type of substitution cipher in which each letter
* in the plaintext is replaced by a letter some fixed number of positions down the alphabet. /
*
* @author FAHRI YARDIMCI
* @author khalil2535
*/
public
class
Caesar
{
/**
* Encrypt text by shifting every Latin char by add number shift for ASCII Example : A + 1 -> B
*
* @param message
* @param shift
* @return Encrypted message
*/
public
static
String
encode
(
String
message
,
int
shift
) {
String
encoded
=
""
;
shift
%=
26
;
final
int
length
=
message
.
length
();
for
(
int
i
=
0
;
i
<
length
;
i
++) {
// int current = message.charAt(i); //using char to shift characters because ascii
// is in-order latin alphabet
char
current
=
message
.
charAt
(
i
);
// Java law : char + int = char
if
(
IsCapitalLatinLetter
(
current
)) {
current
+=
shift
;
encoded
+= (
char
) (
current
>
'Z'
?
current
-
26
:
current
);
// 26 = number of latin letters
}
else
if
(
IsSmallLatinLetter
(
current
)) {
current
+=
shift
;
encoded
+= (
char
) (
current
>
'z'
?
current
-
26
:
current
);
// 26 = number of latin letters
}
else
{
encoded
+=
current
;
}
}
return
encoded
;
}
/**
* Decrypt message by shifting back every Latin char to previous the ASCII Example : B - 1 -> A
*
* @param encryptedMessage
* @param shift
* @return message
*/
public
static
String
decode
(
String
encryptedMessage
,
int
shift
) {
String
decoded
=
""
;
shift
%=
26
;
final
int
length
=
encryptedMessage
.
length
();
for
(
int
i
=
0
;
i
<
length
;
i
++) {
char
current
=
encryptedMessage
.
charAt
(
i
);
if
(
IsCapitalLatinLetter
(
current
)) {
current
-=
shift
;
decoded
+= (
char
) (
current
<
'A'
?
current
+
26
:
current
);
// 26 = number of latin letters
}
else
if
(
IsSmallLatinLetter
(
current
)) {
current
-=
shift
;
decoded
+= (
char
) (
current
<
'a'
?
current
+
26
:
current
);
// 26 = number of latin letters
}
else
{
decoded
+=
current
;
}
}
return
decoded
;
}
/**
* @param c
* @return true if character is capital Latin letter or false for others
*/
private
static
boolean
IsCapitalLatinLetter
(
char
c
) {
return
c
>=
'A'
&&
c
<=
'Z'
;
}
/**
* @param c
* @return true if character is small Latin letter or false for others
*/
private
static
boolean
IsSmallLatinLetter
(
char
c
) {
return
c
>=
'a'
&&
c
<=
'z'
;
}
public
static
void
main
(
String
[]
args
) {
Scanner
input
=
new
Scanner
(
System
.
in
);
System
.
out
.
println
(
"Please enter the message (Latin Alphabet)"
);
String
message
=
input
.
nextLine
();
System
.
out
.
println
(
message
);
System
.
out
.
println
(
"Please enter the shift number"
);
int
shift
=
input
.
nextInt
() %
26
;
System
.
out
.
println
(
"(E)ncode or (D)ecode ?"
);
char
choice
=
input
.
next
().
charAt
(
0
);
switch
(
choice
) {
case
'E'
:
case
'e'
:
System
.
out
.
println
(
"ENCODED MESSAGE IS
\n
"
+
encode
(
message
,
shift
));
// send our function to handle
break
;
case
'D'
:
case
'd'
:
System
.
out
.
println
(
"DECODED MESSAGE IS
\n
"
+
decode
(
message
,
shift
));
default
:
System
.
out
.
println
(
"default case"
);
}
input
.
close
();
}
}
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