字符串类练习

模拟登陆功能 题目：模拟登陆，给三次机会，如果密码输入错误，提示还有几次

package DEMO2.DAY10_demo06_练习_模拟登陆;
import java.util.Scanner;


public class Demo {
    public static void main(String[] args) {
        String username = "admin";
        String password = "admin";
        Scanner sc = new Scanner(System.in);
        for (int i = 1; i <= 3; i++) {
            System.out.println("请输入用户名:");
            String inputusername = sc.next();
            System.out.println("请输入密码:");
            String inputpassword = sc.next();

            if (username.equals(inputusername) && password.equals(inputpassword)) {
                System.out.println("登陆成功");
                break;
            } else {
                if (i == 3) {
                    System.out.println("三次机会已用完，账号锁定");
                } else {
                    System.out.println("用户名或密码错误，你还有" + (3 - i) + "次机会");
                }
            }
        }
    }
}

首字母转大写 需求：把一个字符串的首字母转成大写，其余为小写。(只考虑英文大小写字母字符)

package DEMO2.DAY10_demo07_练习_首字母转大写;

public class Demo {
    public static void main(String[] args) {
        String s1 = "abcd";
        //获取第一个字母
        String s2 = s1.substring(0,1);
        System.out.println(s2);

        //获取第二个字符串之后的值
        String s3 = s1.substring(1);
        System.out.println(s3);

        //拼接结果
        String result = s2.toUpperCase()+s3.toLowerCase();
        System.out.println("拼接之后的结果："+result);
    }
}

数组转字符串 需求：把数组中的数据按照指定个格式拼接成一个字符串

package DEMO2.DAY10_demo08_练习_数组转字符串;
public class Demo {
    public static void main(String[] args) {
        int[] arr = {1,2,3};
        //"[1, 2, 3]"
        String result = "[";
        for (int i = 0; i < arr.length; i++) {
            if(i == arr.length-1) {
                result += arr[i]+" ";
            }else{
                result += arr[i]+", ";
            }
        }
        result += "]";
        System.out.println(result);
    }
}

字符串反转 需求：把字符串反转           举例：键盘录入"abc"           输出结果："cba"

package DEMO2.DAY10_demo09_练习_字符串反转;
public class Demo {
    public static void main(String[] args) {
        String s1 = "abc";

        for (int i = s1.length()-1; i >=0 ; i--) {
            System.out.print(s1.charAt(i));
        }
    }
}

统计字符的个数 题目：获取指定字符串中，大写字母、小写字母、数字的个数。

package DEMO2.DAY10_demo10_练习_统计字符的个数;

public class Demo {
    public static void main(String[] args) {
        String s1 = "EDGabcD999";
        int bigCount = 0;//大写
        int smallCount = 0;//小写
        int numberCount = 0;//数字


        for (int i = 0; i < s1.length(); i++) {
            char charI = s1.charAt(i);
            //ascii
            //charI >= 65 && charI <= 90
             if(charI >= 'A' && charI <='Z'){
                 bigCount ++;
             }else if(charI >= 'a' && charI <= 'z'){
                 smallCount ++;
             }else{
                 numberCount ++;
             }
        }
        System.out.println("大写: "+bigCount);
        System.out.println("小写: "+smallCount);
        System.out.println("数字: "+numberCount);
    }
}

大串中查找小串出现的次数 需求：查询大字符串中，出现指定小字符串的次数。 代码1

package DEMO2.DAY10_demo11_练习_大串中查找小串出现的次数;

public class Demo {
    public static void main(String[] args) {
        String c = "woaijavawoaijavawoaijavawoaijavahhhjava";
        //"java"
        //找到第一次出现的下标  4
        //int index =s.indexOf("java");
        //System.out.println(index);
        int count = getCount("java", c);
        System.out.println(count);
    }
    public static int getCount(String target,String s){
        //记录出现的次数
        int count = 0;
        //查找第一次出现的位置
        int index = s.indexOf(target);
        //如果还存在字符串
        while(index !=-1){
            count++;//次数+1
            //第一次循环：woaijavawoaijavawoaijavawoaijavahhhjava
            //第二次循环：woaijavawoaijavawoaijavahhhjava
            //第三次循环：woaijavawoaijavahhhjava
            s= s.substring(index+target.length());
            index =s.indexOf(target);
        }
        return count;
    }
}

最终的代码

package DEMO2.DAY10_demo11_练习_大串中查找小串出现的次数;

public class Demo {
    public static void main(String[] args) {
        String c = "woaijavawoaijavawoaijavawoaijavahhhjava";
        //"java"
        //找到第一次出现的下标  4
        //int index =s.indexOf("java");
        //System.out.println(index);
        int count = getCount("java", c);
        System.out.println(count);
    }
    public static int getCount(String target,String s){
        //记录出现的次数
        int count = 0;
        //查找第一次出现的位置
        int index = 0;//s.indexOf(target);
        //如果还存在字符串
        //将index的赋值放到循环的判断条件里面
        while((index =s.indexOf(target)) !=-1){
            count++;//次数+1
            //第一次循环：woaijavawoaijavawoaijavawoaijavahhhjava
            //第二次循环：woaijavawoaijavawoaijavahhhjava
            //第三次循环：woaijavawoaijavahhhjava
            s= s.substring(index+target.length());
//          index =s.indexOf(target);
        }
        return count;
    }
}