Interactive CLI for selective file copying with content preview. Built with Java 25 as a single-file unnamed class.

# Interactive mode
java ZFSL.java

# Command line mode
java ZFSL.java -s ./src -t ./backup -e .java

-s, --source <directory>     Source directory (default: current directory)
-t, --target <directory>     Target directory (prompts if not provided)
-e, --extension <extension>  File extension filter (prompts if not provided)
-h, --help                   Display help

For each discovered file:

1. Preview first 20 lines with metadata (size, last modified)
2. Choose: y (copy), n (skip), or q (quit)
3. Confirm overwrite if target file exists
4. View operation summary with detailed error report

Requirements: Java 25+

Design:

• Single file unnamed class
• Zero dependencies (Java SE only)
• Records for immutable data (Config, ProcessingState)
• Sealed interfaces for type-safe result handling (OperationResult, UserAction)
• Pattern matching in switch expressions
• Text blocks for multi-line output

Key Components:

• Config: Validates source/target directories and normalizes file extensions
• OperationResult: Success/Skip/Error outcomes with detailed context
• ProcessingState: Tracks file counts and results, formats summary reports
• UserAction: Copy/Skip/Quit decisions from user input

File Operations:

• Recursive discovery via Files.walk()
• Flat copy structure (no subdirectories preserved)
• Overwrites only with explicit confirmation
• Specific error messages for AccessDeniedException, FileSystemException, etc.

# Copy Java files from src to backup
java ZFSL.java -s ./src -t ./backup -e .java

# Interactive selection from current directory
java ZFSL.java -t ./output -e txt