we can use abstract class and interface together

When to Use Both Abstract Class and Interface Together

You need to allow multiple inheritance of behavior (via interfaces), but also want to share default behavior

we use this pattern to build libraries and frameworks

interface LoggerInterface {
    public function log(string $message);
}

interface FileWritable {
    public function writeToFile(string $filename);
}

abstract class LoggerBase implements LoggerInterface {
    // Shared property
    protected string $logLevel = 'INFO';

    // Concrete method
    public function setLogLevel(string $level) {
        $this->logLevel = $level;
    }

    // Abstract method from LoggerInterface
    abstract public function log(string $message);
}

// Concrete class that uses both abstract class and interface
class FileLogger extends LoggerBase implements FileWritable {

    public function log(string $message) {
        echo "[{$this->logLevel}] $message\n";
    }

    public function writeToFile(string $filename) {
        file_put_contents($filename, "[{$this->logLevel}] Logging to file\n", FILE_APPEND);
    }
}

// Usage
$logger = new FileLogger();
$logger->setLogLevel('DEBUG');
$logger->log("This is a debug message.");
$logger->writeToFile("log.txt");