查看“正则表达式元字符定位符”的源代码

https://www.bilibili.com/video/BV1Eq4y1E79W?p=12

定位符，规定要匹配的字符串出现的位置，比如在字符串的开始还是在结束的位置
{| class="wikitable"
!符号
!含义
!示例
!说明
!匹配输入
|-
|^
|指定起始字符
|^[0-9]+[a-z]*
|以至少1个数字开头，后接任意个小写字母的字符串
|123、6aa、555edf
|-
|$
|指定结束字符
|^[0-9]\\-[a-z]+$
|以1个数字开头后接连字符"-"，并以至少1个小写字母结尾的字符串
|1-a
|-
|\\b
|匹配目标字符串的边界
|han\\b
|这里说的字符串边界指的是子串间有空格，或者是目标字符串的结束位置；
既可以是字符串的最后，也可是空格前面的子串
|hanshunping sp<u>han</u> nn<u>han</u>
|-
|\\B
|匹配目标字符串的非边界
|han\\B
|和\\b的含义刚刚相反
|<u>han</u>shunping sphan nnhan
|}

=== 示例：在 "123abc" 中找 ^[0-9]+[a-z]* ===
<syntaxhighlight lang="java">
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegExp06 {

    public static void main(String[] args) {

        String content = "123abc";

        //以至少1个数字开头，后接任意个小写字母的字符串
        String regStr = "^[0-9]+[a-z]*";

        Pattern pattern = Pattern.compile(regStr);

        Matcher matcher = pattern.matcher(content);

        while (matcher.find()) {

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

        }


    }

}
</syntaxhighlight><syntaxhighlight lang="console">
找到：123abc
</syntaxhighlight>^[0-9]只匹配数字开头





=== 示例：在 "a123abc" 中找 ^[0-9]+[a-z]* ===
<syntaxhighlight lang="java">
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegExp06 {

    public static void main(String[] args) {

        String content = "a123abc";

        //以至少1个数字开头，后接任意个小写字母的字符串
        String regStr = "^[0-9]+[a-z]*";

        Pattern pattern = Pattern.compile(regStr);

        Matcher matcher = pattern.matcher(content);

        while (matcher.find()) {

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

        }


    }

}
</syntaxhighlight>控制台没有输出，因为 content 不再是数字字符开头




=== 示例：在 "123abc12" 中找 ^[0-9]+[a-z]* ===
<syntaxhighlight lang="java">
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegExp06 {

    public static void main(String[] args) {

        String content = "123abc12";

        //以至少1个数字开头，后接任意个小写字母的字符串
        String regStr = "^[0-9]+[a-z]*";

        Pattern pattern = Pattern.compile(regStr);

        Matcher matcher = pattern.matcher(content);

        while (matcher.find()) {

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

        }


    }

}
</syntaxhighlight><syntaxhighlight lang="console">
找到：123abc
</syntaxhighlight>




=== 示例：在 "123" 中找 ^[0-9]+[a-z]* ===
<syntaxhighlight lang="java">
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegExp06 {

    public static void main(String[] args) {

        String content = "123";

        //以至少1个数字开头，后接任意个小写字母的字符串
        String regStr = "^[0-9]+[a-z]*";

        Pattern pattern = Pattern.compile(regStr);

        Matcher matcher = pattern.matcher(content);

        while (matcher.find()) {

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

        }


    }

}
</syntaxhighlight><syntaxhighlight lang="console">
找到：123
</syntaxhighlight>




=== 示例：在 "123abc12" 中找 ^[0-9]+[a-z]+$ ===
<syntaxhighlight lang="java">
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegExp06 {

    public static void main(String[] args) {

        String content = "123abc12";

        //以至少1个数字开头，必须以至少1个小写字母结束
        String regStr = "^[0-9]+[a-z]+$";

        Pattern pattern = Pattern.compile(regStr);

        Matcher matcher = pattern.matcher(content);

        while (matcher.find()) {

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

        }


    }

}
</syntaxhighlight>控制台什么也不输出，因为正则表达式要求 内容字符串必须以至少1个小写字母结束


=== 示例：在 "123abc" 中找 ^[0-9]+[a-z]+$ ===
<syntaxhighlight lang="java">
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegExp06 {

    public static void main(String[] args) {

        String content = "123abc";

        //以至少1个数字开头，必须以至少1个小写字母结束
        String regStr = "^[0-9]+[a-z]+$";

        Pattern pattern = Pattern.compile(regStr);

        Matcher matcher = pattern.matcher(content);

        while (matcher.find()) {

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

        }


    }

}
</syntaxhighlight><syntaxhighlight lang="console">
找到：123abc
</syntaxhighlight>




=== 示例：在 "123" 中找 ^[0-9]+[a-z]+$ ===
<syntaxhighlight lang="java">
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegExp06 {

    public static void main(String[] args) {

        String content = "123";

        //以至少1个数字开头，必须以至少1个小写字母结束
        String regStr = "^[0-9]+[a-z]+$";

        Pattern pattern = Pattern.compile(regStr);

        Matcher matcher = pattern.matcher(content);

        while (matcher.find()) {

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

        }
        
    }

}
</syntaxhighlight>控制台什么也不输出，因为正则表达式要求 内容字符串必须以至少1个小写字母结束




=== 示例：在 "123a" 中找 ^[0-9]+[a-z]+$ ===
<syntaxhighlight lang="java">
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegExp06 {

    public static void main(String[] args) {

        String content = "123a";

        //以至少1个数字开头，必须以至少1个小写字母结束
        String regStr = "^[0-9]+[a-z]+$";

        Pattern pattern = Pattern.compile(regStr);

        Matcher matcher = pattern.matcher(content);

        while (matcher.find()) {

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

        }

    }

}
</syntaxhighlight><syntaxhighlight lang="console">
找到：123a
</syntaxhighlight>




=== 示例：在 "123abc" 中找 ^[0-9]+\\-[a-z]+$ ===
<syntaxhighlight lang="java">
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegExp06 {

    public static void main(String[] args) {

        String content = "123abc";

        //以至少1个数字开头，必须以至少1个小写字母结束，同时中间有连字符(减)-
        String regStr = "^[0-9]+\\-[a-z]+$";

        Pattern pattern = Pattern.compile(regStr);

        Matcher matcher = pattern.matcher(content);

        while (matcher.find()) {

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

        }

    }

}
</syntaxhighlight>控制台什么也不输出，因为正则表达式要求被匹配内容中间还要有连字符（减号）-




=== 示例：在 "123-abc" 中找 "^[0-9]+\\-[a-z]+$" ===
<syntaxhighlight lang="java">
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegExp06 {

    public static void main(String[] args) {

        String content = "123-abc";

        //以至少1个数字开头，必须以至少1个小写字母结束，同时中间有连字符(减)-
        String regStr = "^[0-9]+\\-[a-z]+$";

        Pattern pattern = Pattern.compile(regStr);

        Matcher matcher = pattern.matcher(content);

        while (matcher.find()) {

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

        }

    }

}
</syntaxhighlight><syntaxhighlight lang="console">
找到：123-abc
</syntaxhighlight>



=== 示例：在 "hanshunping sphan nnhan" 中找 "han\\b" ===
<syntaxhighlight lang="java">
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegExp06 {

    public static void main(String[] args) {

        String content = "hanshunping sphan nnhan";

        //表示匹配边界的han
        String regStr = "han\\b";

        Pattern pattern = Pattern.compile(regStr);

        Matcher matcher = pattern.matcher(content);

        while (matcher.find()) {

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

        }

    }

}
</syntaxhighlight><syntaxhighlight lang="console">
找到：han
找到：han
</syntaxhighlight>



=== 示例：在 "hanshunping sphan nnhanu" 中找 "han\\b" ===
<syntaxhighlight lang="java">
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegExp06 {

    public static void main(String[] args) {

        String content = "hanshunping sphan nnhanu";

        //表示匹配边界的han
        String regStr = "han\\b";

        Pattern pattern = Pattern.compile(regStr);

        Matcher matcher = pattern.matcher(content);

        while (matcher.find()) {

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

        }

    }

}
</syntaxhighlight><syntaxhighlight lang="console">
找到：han
</syntaxhighlight>





=== 示例：在 "hanshunping sphan nnhan" 中找 "han\\B" ===
<syntaxhighlight lang="java">
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegExp06 {

    public static void main(String[] args) {

        String content = "hanshunping sphan nnhan";

        //和 \\b 的含义刚好相反
        String regStr = "han\\B";

        Pattern pattern = Pattern.compile(regStr);

        Matcher matcher = pattern.matcher(content);

        while (matcher.find()) {

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

        }

    }

}
</syntaxhighlight><syntaxhighlight lang="console">
找到：han
</syntaxhighlight>