【JAVA学习笔记】52 - 本章作业

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项目代码

https://github.com/yinhai1114/Java_Learning_Code/tree/main/IDEA_Chapter13/src/com/yinhai/wrapper_/homework_

1.字符反转

 注意String是final的不能改变需要toCharArray改成char数组

返回String需要将char改成valueOf改为String

public class HomeWork01 {public static void main(String[] args) {String str = "0123456789";//改变的是char，和str无关try {System.out.println(reverse(str,1,5));//0543216789System.out.println(reverse(str,4,5));//0123546789System.out.println(reverse(str,2,5));//0154326789System.out.println(reverse(str,7,5));//0154326789} catch (Exception e) {System.out.println(e.getMessage());return;}//想改变str直接str = rever(str,start,end);即可}public static String reverse(String str,int start,int end){//需要对输入的参数做一个验证if(!(str.length() > end && end > start && start > 0 && str!=null)){throw new RuntimeException("参数不正确");}char[] chars = str.toCharArray();//返回的是new的char temp;for (int i = 0; i < (end - start) / 2 + 1; i++) {if(start + i == end + i){break;}temp = chars[start + i];chars[start + i]= chars[end - i];chars[end - i] = temp;}String str1 = String.valueOf(chars);return str1;}
}

 

和老师的代码原理大差不差

public class Homework01 {public static void main(String[] args) {//测试String str = "abcdef";System.out.println("===交换前===");System.out.println(str);try {str = reverse(str, 1, 4);} catch (Exception e) {System.out.println(e.getMessage());return;}System.out.println("===交换后===");System.out.println(str);}/*** (1) 将字符串中指定部分进行反转。比如将"abcdef"反转为"aedcbf"* (2) 编写方法 public static String reverse(String  str, int start , int end) 搞定* 思路分析* (1) 先把方法定义确定* (2) 把 String 转成 char[] ，因为char[] 的元素是可以交换的* (3) 画出分析示意图* (4) 代码实现*/public static String reverse(String str, int start, int end) {//对输入的参数做一个验证//老韩重要的编程技巧分享!!!//(1) 写出正确的情况//(2) 然后取反即可//(3) 这样写，你的思路就不乱if(!(str != null && start >= 0 && end > start && end < str.length())) {throw new RuntimeException("参数不正确");}char[] chars = str.toCharArray();char temp = ' '; //交换辅助变量for (int i = start, j = end; i < j; i++, j--) {temp = chars[i];chars[i] = chars[j];chars[j] = temp;}//使用chars 重新构建一个String 返回即可return new String(chars);}
}

2.异常处理

public class HomeWork02 {public static void main(String[] args) {Person person = new Person();while (!person.enterInfo()) {}}
}class Person {Scanner scanner = new Scanner(System.in);private String name;private String password;private String mail;public Person() {}public boolean enterInfo() {try {System.out.println("请输入名字长度为2 3 4");judeName(scanner.next());System.out.println("请输入六位密码");judePassword(scanner.next());System.out.println("请输入邮箱，带有@以及.且@在.之前");judeMail(scanner.next());} catch (Exception e) {System.out.println(e.getMessage());System.out.println("请重新尝试");return false;}System.out.println("注册成功");return true;}public void judeName(String name) {if (2 <= name.length() && name.length() <= 4) {this.name = name;} else {throw new RuntimeException("名字长度错误");}}public void judePassword(String password) {char[] chars = password.toCharArray();if (chars.length != 6) {throw new RuntimeException("密码长度错误");}for (int i = 0; i < chars.length; i++) {if (!(chars[i] < 58 && chars[i] > 47)){throw new RuntimeException("密码包含非数字元素");}}this.password = String.valueOf(chars);}public void judeMail(String mail) {int index1 = mail.lastIndexOf('@');int index2 = mail.lastIndexOf('.');if (index1 > index2) {throw new RuntimeException("格式错误 @必须在.之前");}if(index1 == -1){throw new RuntimeException("格式错误 必须含有@");}if(index2 == -1){throw new RuntimeException("格式错误 必须含有.");}this.mail = mail;}
}

 老师的代码

public class Homework02 {public static void main(String[] args) {String name = "abc";String pwd = "123456";String email = "ti@i@sohu.com";try {userRegister(name,pwd,email);System.out.println("恭喜你，注册成功~");} catch (Exception e) {System.out.println(e.getMessage());}}/*** 输入用户名、密码、邮箱，如果信息录入正确，则提示注册成功，否则生成异常对象* 要求：* (1) 用户名长度为2或3或4* (2) 密码的长度为6，要求全是数字  isDigital* (3) 邮箱中包含@和.   并且@在.的前面* <p>* 思路分析* (1) 先编写方法 userRegister(String name, String pwd, String email) {}* (2) 针对 输入的内容进行校核，如果发现有问题，就抛出异常，给出提示* (3) 单独的写一个方法，判断 密码是否全部是数字字符 boolean*/public static void userRegister(String name, String pwd, String email) {//再加入一些校验if(!(name != null && pwd != null && email != null)) {throw  new RuntimeException("参数不能为null");}//过关//第一关int userLength = name.length();if (!(userLength >= 2 && userLength <= 4)) {throw new RuntimeException("用户名长度为2或3或4");}//第二关if (!(pwd.length() == 6 && isDigital(pwd))) {throw new RuntimeException("密码的长度为6，要求全是数字");}//第三关int i = email.indexOf('@');int j = email.indexOf('.');if (!(i > 0 && j > i)) {throw new RuntimeException("邮箱中包含@和.   并且@在.的前面");}}//单独的写一个方法，判断 密码是否全部是数字字符 booleanpublic static boolean isDigital(String str) {char[] chars = str.toCharArray();for (int i = 0; i < chars.length; i++) {if (chars[i] < '0' || chars[i] > '9') {return false;}}return true;}}

3.字符串的方法使用

public class HomeWork03 {public static void main(String[] args) {String name = "Yin xiao Hai";printName(name);}public static void printName(String name){if(name == null){System.out.println("不能为空");return;}//对接受的字符串分割String[] str = name.split(" ");if (str.length != 3){System.out.println("输入的字符串格式不对");return;}System.out.println(String.format("%s,%s .%c" ,str[2],str[0],str[1].toUpperCase().charAt(0)));}
}

4. 判断大写小写数字个数

public class HomeWork04 {public static void main(String[] args) {int countA = 0;int counta = 0;int countNum = 0;//转成数组判断String name = "Yinhai#3612";//也可以用str.charAt(i)char[] names = name.toCharArray();for (int i = 0; i < names.length; i++) {if (names[i] <= 'Z' && names[i] >= 'A'){countA++;}if (names[i] <= 'z' && names[i] >= 'a'){counta++;}if (names[i] <= '9' && names[i] >= '0'){countNum++;}}System.out.println("该字符串共有" + countA + "个大写字母"+ counta + "个小写字母" + countNum + "个数字");}
}

5.字符串的内存分布（多看看）

错了一个 没有重写，就是用Object的equals，判断的是地址相等，还错了一个s1==s4看错了，然后就是最后的那个，会使用Builder在常量池内创建新的hellohspedu然后用t1指向value指向该常量池，在前面的String类中有讲，多看看。然后t2直接指向已经有的

public class HomeWork05 {public static void main(String[] args) {String s1 = "hspedu";Animal a = new Animal(s1);Animal b = new Animal(s1);System.out.println(a == b);System.out.println(a.equals(b));System.out.println(a.name == b.name);String s4 = new String("hspedu");String s5 = "hspedu";System.out.println(s1 == s4);System.out.println(s4 == s5);String t1 = "hello" + s1;String t2 = "hellohspedu";System.out.println(t1.intern() == t2);}
}class Animal {String name;public Animal(String name) {this.name = name;}
}

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