Java笔记025-常用类章节练习

常用类章节练习

1、编程题

(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

package com13.exercise;

/**
 * @author 甲柒
 * @version 1.0
 * @title Exercise01
 * @package com13.exercise
 * @time 2023/1/12 18:49
 */
public class Exercise01 {
    public static void main(String[] args) {
        String str = "abcdefgh";
        System.out.println("=====交换前=====");
        System.out.println(str);
        try {
            str = reverse(str, 1, 6);
        } catch (Exception e) {
            System.out.println(e.getMessage());
            return;
        }
        System.out.println("=====交换后=====");
        System.out.println(str);
    }

    public static String reverse(String str, int start, int end) {
        //对输入的参数进行验证
        //(1)写出正确的情况
        //(2)然后取反
        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、编程题

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

(3)邮箱中包含@和.并且@在.的前面isDigital

package com13.exercise;

/**
 * @author 甲柒
 * @version 1.0
 * @title Exercise02
 * @package com13.exercise
 * @time 2023/1/12 19:07
 */
public class Exercise02 {
    public static void main(String[] args) {
        String name = "tom";
        String pwd = "123456";
        String email = "[email protected]";
        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) {
        if (!(name != null && pwd != null && email != null)) {
            throw new RuntimeException("参数不能为空");
        }

        int userLength = name.length();
        if (!(userLength >= 2 && userLength <= 4)) {
            throw new RuntimeException("用户名长度为2或3或4");
        }

        if (!(pwd.length() == 6 && isDigital(pwd))) {
            throw new RuntimeException("密码长度是6，要求全是数字");
        }

        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.前面");
        }
    }

    public 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、编程题

(1)编写java程序，输入形式为：Han Shun Ping的人名，以Ping,Han .S的形式打印

出来。其中.S是中间单词的首字母。

(2)例如输入"Willian Jefferson Clinton"，输出形式为：Clinton,Willia .j

package com13.exercise;

/**
 * @author 甲柒
 * @version 1.0
 * @title Exercise03
 * @package com13.exercise
 * @time 2023/1/12 21:36
 */
public class Exercise03 {
    public static void main(String[] args) {
        String name = "han Shun Ping";
        printName(name);
    }

    public static void printName(String str) {
        if (str == null) {
            System.out.println("str不能为空");
            return;
        }

        String[] names = str.split(" ");
        if (names.length != 3) {
            System.out.println("输入的字符串格式不对");
            return;
        }
        String format = String.format("%s,%s .%s", names[2], names[0], names[1].toUpperCase().charAt(0));
        System.out.println(format);
    }
}

4、编程题

输入字符串，判断里面有多少个大写字母，多少个小写字母，多少个数字

package com13.exercise;

/**
 * @author 甲柒
 * @version 1.0
 * @title Exercise04
 * @package com13.exercise
 * @time 2023/1/12 21:48
 */
public class Exercise04 {
    public static void main(String[] args) {
        String str = "6789qq甲柒DDDxyz";
        countStr(str);
    }

    public static void countStr(String str) {
        if (str == null) {
            System.out.println("输入不能为null");
            return;
        }
        int strLen = str.length();
        int numCount = 0;
        int lowerCount = 0;
        int upperCount = 0;
        int otherCount = 0;
        for (int i = 0; i < strLen; i++) {
            if (str.charAt(i) >= '0' && str.charAt(i) <= '9') {
                numCount++;
            } else if (str.charAt(i) >= 'a' && str.charAt(i) <= 'z') {
                upperCount++;
            } else if (str.charAt(i) >= 'A' && str.charAt(i) <= 'Z') {
                lowerCount++;
            } else {
                otherCount++;
            }
        }
        System.out.println("数字有" + numCount + "个");
        System.out.println("小写字母有" + upperCount + "个");
        System.out.println("大写字母有" + lowerCount + "个");
        System.out.println("其他字符有" + otherCount + "个");
    }
}

5、写出以下运行结果

package com13.exercise;

/**
 * @author 甲柒
 * @version 1.0
 * @title Exercise05
 * @package com13.exercise
 * @time 2023/1/12 21:59
 */
public class Exercise05 {
    public static void main(String[] args) {
        String s1 = "甲柒";
        Animal a = new Animal(s1);
        Animal b = new Animal(s1);
        System.out.println(a == b);//false
        System.out.println(a.equals(b));//false
        System.out.println(a.name == b.name);//true
        String s4 = new String("甲柒");
        String s5 = "甲柒";

        System.out.println(s1 == s4);//false
        System.out.println(s4 == s5);//false

        String t1 = "hello" + s1;
        String t2 = "hello甲柒";
        System.out.println(t1.intern() == t2);//true
        
    }
}

class Animal {
    String name;

    public Animal(String name) {
        this.name = name;
    }
}