练习 String翻转 注册处理 字符串统计

p493

将字符串中指定部分进行翻转

package chapter;public class reverse {public static void main(String[] args) {String str = "abcdef";str = reverseMethod(str,0,3);System.out.println(str);}public static String reverseMethod(String str, int start, int end) {char[] chars = str.toCharArray();char temp = ' ';for (int i = start, j = end; i < j; i++, j--) {temp = chars[i];chars[i] = chars[j];chars[j] = temp;}return new String(chars);}
}

输入用户名，密码，邮箱，输入正确，则提示注册成功，否则生成异常对象

package chapter;public class HomeWork {public static void main(String[] args) {String name = "asd";String pwd = "548745";String email= "[e-mail]";try {userRegister(name,pwd,email);System.out.println("注册成功");} catch (Exception e) {System.out.println(e.getMessage());;}}public static void userRegister(String name,String pwd,String email){// 用户名if(!(name.length()>=2 && name.length()<=4)){throw new RuntimeException("用户名长度错误");}// 密码if(!(pwd.length()==6 && isDigital(pwd) )){throw new RuntimeException("密码错误");}//邮箱int i = email.indexOf('@');int j = email.indexOf('.');if(!(i>0 && j>i)){throw new RuntimeException("邮箱错误");}}//判断密码是否全是数字public static boolean isDigital(String str){char [] chars = str.toCharArray();for (int i = 0; i < str.length(); i++) {if(chars[i] < '0' || chars[i] >'9'){return false;}}return true;}
}

输入 Tony Smith Willam 输出 Willam  Tony W