java regex tester example

### tutorial: java regex tester

#### 1. **getting started with java regex**

to use regex in java, you typically work with two classes:
- `pattern`: represents a compiled regex pattern.
- `matcher`: used to perform matching operations on the text using the `pattern`.

#### 2. **basic regex syntax**

- `.`: matches any character except a newline.
- `*`: matches zero or more occurrences of the preceding element.
- `+`: matches one or more occurrences of the preceding element.
- `?`: matches zero or one occurrence of the preceding element.
- `^`: matches the beginning of the input.
- `$`: matches the end of the input.
- `[]`: matches any one of the enclosed characters.
- `|`: acts as a logical or.
- `\`: escapes special characters.

#### 3. **example code**

here’s a simple java program that demonstrates how to use regex for validating email addresses.

#### 4. **explanation of the code**

- **regex pattern**: the regex used in the `isvalidemail` method is designed to match standard email formats. it allows for:
- alphanumeric characters, underscores, pluses, ampersands, and hyphens in the local part.
- an "@" symbol separating the local part from the domain.
- valid domain names, including subdomains.

- **pattern and matcher**:

#### 5. **running the code**

to run the above code:
2. open your terminal/command prompt.
3. compile the java file with:

4. run the compiled class with:


#### 6. **expected output**

when ...

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