java regex find and replace

- **pattern**: a compiled representation of a regular expression.
- **matcher**: an engine that performs matching operations on an input string using a `pattern`.
- **patternsyntaxexception**: an unchecked exception thrown to indicate a syntax error in a regular expression pattern.

### finding and replacing with regex in java

the `matcher` class provides methods to find and replace substrings in a string based on a specified regex pattern. the most commonly used methods for replacement are:

- `replaceall(string replacement)`: replaces each substring of the input sequence that matches the pattern with the given replacement string.
- `replacefirst(string replacement)`: replaces the first substring of the input sequence that matches the pattern with the given replacement string.

### basic syntax of regex

- `.`: matches any character except a line terminator.
- `*`: 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 any single character within the brackets.
- `^`: matches the beginning of the input.
- `$`: matches the end of the input.
- `\\d`: matches any digit (equivalent to [0-9]).
- `\\w`: matches any word character (equivalent to [a-za-z0-9_]).
- `\\s`: matches any whitespace character.

### example: finding and replacing strings

let's create a simple java program that demonstrates how to find and replace substrings in a string using regex.

#### example code

### explanation of the code

2. **input string**: we define a string `input` that contains the text where we wan ...

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