caesar.java

凯撒加密算法 *此算法中区分了字母的大小写,并可以保留标点符号

/*
*凯撒加密算法
*此算法中区分了字母的大小写,并可以保留标点符号
*/
public class Caesar 
{
	int key = 3;
	public String getCipher(String message)//to encrypt
	{
		char msgChar [] = message.toCharArray();
		int len = msgChar.length;
		char cipChar [] = new char[len];
		for (int i=0; i<len ;i++ )
		{
			cipChar[i] = convert(msgChar[i],1);
		}
		String cipher = new String(cipChar);
		return cipher;
	}
	public String getMessage(String cipher)//to decode
	{
		char cipChar[] = cipher.toCharArray();
		int len = cipChar.length;
		char msgChar[] = new char[len];
		for (int i=0 ; i<len ;i++ )
		{
			msgChar[i] = convert(cipChar[i],-1);
		}
		String message = new String(msgChar);
		return message;
	}
	public char convert(char c , int op)//when op = 1 stands for encrypting , when op = -1 stands for decoding
	{
		int num = (int)c;
		
		if (num>=65 && num<=90)//if it is up case
		{
			int res = num + key*op;
			if (res > 90)//test whether the number is out of bound
				res = res-26;
			else if (res <65)
				res = res+26;
			return (char)res;
		}
		else if (num>=97 && num<=122)//if it is low case
		{
			int res = num + key*op;
			if (res > 122)//test whether the number is out of bound
				res = res-26;
			else if (res <97)
				res = res+26;
			return (char)res;
		}
		else
		{
			return c;
		}
	}
	/*
	*test if correct
	*/
	public static void main(String [] args)
	{
		Caesar caesar = new Caesar();
		String message = new String("For test!");
		String cipher = caesar.getCipher(message);
		System.out.println("The Cipher is:  "+cipher);
		message = caesar.getMessage(cipher);
		System.out.println("The Message is: "+message);
	}
}