java regex test string

### 1. understanding regex syntax

before we dive into the code, let's review some basic regex syntax:

- `.` - matches any character except a line terminator.
- `*` - matches 0 or more occurrences of the preceding element.
- `+` - matches 1 or more occurrences of the preceding element.
- `?` - matches 0 or 1 occurrence of the preceding element.
- `[]` - matches any single character within the brackets.
- `^` - anchors the match to the start of the string.
- `$` - anchors the match to the end of the string.
- `\\d` - matches any digit (equivalent to [0-9]).
- `\\d` - matches any non-digit.
- `\\w` - matches any word character (alphanumeric + underscore).
- `\\w` - matches any non-word character.
- `\\s` - matches any whitespace character (space, tab, newline).
- `\\s` - matches any non-whitespace character.

### 2. using the `pattern` and `matcher` classes

in java, regex operations primarily involve two classes: `pattern` and `matcher`.

- **pattern**: a compiled representation of a regex.
- **matcher**: an engine that performs matching operations on a character sequence using a pattern.

### 3. testing a string with regex

here’s a simple example showing how to test if a string matches a regex pattern. we'll check if a string is a valid email address.

#### example code

### 4. explanation of the code

2. **defining the email regex**: the regex pattern `^[a-za-z0-9._%+-]+@[a-za-z0-9.-]+\\.[a-za-z]{2,}$` is defined to match a typical email format.

4. **creati ...

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