正则表达式方括号的应用

https://www.bilibili.com/video/BV1Eq4y1E79W/?p=17 16:50

示例：普通的 .

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class TestTemp {

    public static void main(String[] args) {

        String content = "hello abc 111";

        String regStr = "."; //匹配除了 \n 的所有字符

        Pattern pattern = Pattern.compile(regStr);

        Matcher matcher = pattern.matcher(content);

        while (matcher.find()) {

            System.out.println("找到：" + matcher.group(0));

        }

    }

}

找到：h
找到：e
找到：l
找到：l
找到：o
找到： 
找到：a
找到：b
找到：c
找到： 
找到：1
找到：1
找到：1

示例：[.] 中的 .

示例1：在"hello abc 111"中搜索"[.]"

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class TestTemp {

    public static void main(String[] args) {

        String content = "hello abc 111";

        String regStr = "[.]"; //匹配 . 本身

        Pattern pattern = Pattern.compile(regStr);

        Matcher matcher = pattern.matcher(content);

        while (matcher.find()) {

            System.out.println("找到：" + matcher.group(0));

        }

    }

}

控制台什么都不输出

示例2：示例1：在"hello abc 11.1"中搜索"[.]"

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class TestTemp {

    public static void main(String[] args) {

        String content = "hello abc 11.1";

        String regStr = "[.]"; //匹配 . 本身

        Pattern pattern = Pattern.compile(regStr);

        Matcher matcher = pattern.matcher(content);

        while (matcher.find()) {

            System.out.println("找到：" + matcher.group(0));

        }

    }

}

找到：.

示例3：相当于在"hello abc 11.1"中搜索"\\."

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class TestTemp {

    public static void main(String[] args) {

        String content = "hello abc 11.1";

        String regStr = "\\."; //匹配 . 本身

        Pattern pattern = Pattern.compile(regStr);

        Matcher matcher = pattern.matcher(content);

        while (matcher.find()) {

            System.out.println("找到：" + matcher.group(0));

        }

    }

}

找到：.

示例：在"hello abc 11.1"中搜索"[?]"

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class TestTemp {

    public static void main(String[] args) {

        String content = "hello abc 11.1";

        String regStr = "[?]"; //匹配 . 本身

        Pattern pattern = Pattern.compile(regStr);

        Matcher matcher = pattern.matcher(content);

        while (matcher.find()) {

            System.out.println("找到：" + matcher.group(0));

        }

    }

}

控制台什么都不会输出