复制代码代码如下:
public class Caesar {
public static final String SOURCE = "abcdefghijklmnopqrstuvwxyz";
public static final int LEN = SOURCE.length();
/**
* @param args
*/
public static void main(String[] args) {
String result = caesarEncryption("newyork");
System.out.println("encryption result:" + result);
System.out.println("decryption result:" + caesarDecryption(result));
}
//Encryption
public static String caesarEncryption(String s) {
StringBuilder sb = new StringBuilder();
if (s == null || s.length() < 1) {
System.out.println("you Input nothing.");
return null;
}
if (!isAlp(s)) {
System.out.println("input ABC... only");
return null;
}
s = s.toLowerCase();
int len = s.length();
for (int j = 0; j < len; j++) {
char c = s.charAt(j);
int a = SOURCE.indexOf(c);
if (a == LEN -1) a = -1;
if (a == LEN -2) a = -2;
if (a == LEN - 3) a = -3;
sb.append(SOURCE.charAt(a + 3));
}
return sb.toString();
}
//Decryption
public static String caesarDecryption(String s) {
StringBuilder sb = new StringBuilder();
if (s == null || s.length() < 1) {
System.out.println("you Input nothing.");
return null;
}
if (!isAlp(s)) {
System.out.println("input ABC... only");
return null;
}
s = s.toLowerCase();
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
int a = SOURCE.indexOf(c);
if (a == 2) a = LEN + 2;
if (a == 1) a = LEN + 1;
if (a == 0) a = LEN;
sb.append(SOURCE.charAt(a - 3));
}
return sb.toString();
}
public static boolean isAlp(String s) {
String p = "^[A-Za-z]+$";
Pattern pattern = Pattern.compile(p);
Matcher matcher = pattern.matcher(s);
if (matcher.find()) {
return true;
}
return false;
}
}