替代算法

 老师布置的作业，哈，保存到网上。

package net.as.cn;/** * 2013.3.22 am 替换算法 *  * @author chenas *  */public class MyTiHuan {public final int smalla = 97;public final int bigA = 65;public final int smallz = 122;public final int bigZ = 90;public final int space = 32;public final int smallZero = 96;public final int bigZero = 64;/** * 判断是否为小写字母 *  * @param a * @return */public boolean isSmall(char a) {if (a >= 97 && a <= 122) {return true;} elsereturn false;}/** * 判断是否为大写字母 *  * @param A * @return */public boolean isBig(char A) {if (A >= 65 && A <= 90) {return true;} elsereturn false;}/** * 判断是否为空格 *  * @param spa * @return */public boolean isSpace(char spa) {if (spa == space) {return true;} elsereturn false;}/** * 检查非法字符 *  * @param a * @return */public boolean isPass(char a) {if (a == space) {return true;} else if (a >= smalla && a <= smallz) {return true;} else if (a >= bigA && a <= bigZ) {return true;}return false;}/** *  * 加密 *  * @param mingwen *            明文 * @param yiwei *            右移的位数 * @return 密文 *  */public String enCode(String mingwen, int yiwei) {StringBuffer sBuff = new StringBuffer();char[] mw = mingwen.toCharArray();for (int i = 0; i < mw.length; i++) {char temp = 'a';char c = mw[i];if (isPass(c)) {if (isSmall(c)) {temp = (char) (c + yiwei);if (!isPass(temp)) {temp = (char) (temp - smallz + smallZero);}} else if (isBig(c)) {temp = (char) (c + yiwei);if (!isPass(temp)) {temp = (char) (temp - bigZ + bigZero);}} else if (isSpace(c)) {temp = c;}} else {return sBuff.append("输入中带有非法字符！").toString();}sBuff.append(temp);}return sBuff.toString();}/** * 解密 *  * @param miwen *            密文 * @param yiwei *            左移的位数 * @return 明文 */public String deCode(String miwen, int yiwei) {StringBuffer sBuff = new StringBuffer();char[] mw = miwen.toCharArray();for (int i = 0; i < mw.length; i++) {char temp = 'a';char c = mw[i];if (isPass(c)) {if (isSmall(c)) {temp = (char) (c - yiwei);if (!isPass(temp)) {temp = (char) (smallz - smallZero + temp);}} else if (isBig(c)) {temp = (char) (c - yiwei);if (!isPass(temp)) {temp = (char) (bigZ - bigZero + temp);}} else if (isSpace(c)) {temp = c;}} else {return sBuff.append("密文中带有非法字符！").toString();}sBuff.append(temp);}return sBuff.toString();}public static void main(String[] args) {MyTiHuan mt = new MyTiHuan();String miw = mt.enCode("My name is Jack", 3);System.out.println(miw);String mingw = mt.deCode(miw, 3);System.out.println(mingw);}}