In PHP, Regular Expressions are sequences of characters that form a search pattern, used mainly for text manipulation. Regular expressions provide a powerful and flexible way to search, match, and manipulate strings based on specific patterns. They can be used for tasks such as validating inputs, extracting data, performing string substitutions, and more. Regular expressions enable developers to define complex search patterns and apply them to strings, making it easier to work with textual data. Learn more: https://www.php.net/manual/en/book.regex.php

FTP functions in PHP have various use cases. Some common ones include uploading files to an FTP server, downloading files from an FTP server, synchronizing local and remote directories, retrieving directory listings, creating or deleting directories on an FTP server, and performing other file transfer operations. FTP functions enable PHP scripts to automate file transfers, backup data to remote servers, retrieve files from external sources, or build applications that interact with FTP servers. They provide flexibility and control over file transfer operations in PHP programming.

To check if a variable is an integer in PHP, you can use the is_int() function. The is_int() function checks if a variable is of type integer. It returns true if the variable is an integer and false otherwise. This function is useful when you specifically need to verify that a variable is of integer type. Learn more: https://www.php.net/manual/en/function.is-int.php

To move an uploaded file to a specific directory in PHP, you can utilize the move_uploaded_file() function. This function moves the file to the desired directory. Check out: http://php.net/manual/en/function.move-uploaded-file.php

PHP does indeed support both single-line and multi-line comments. Single-line comments can be denoted by double slashes (//) or a hash symbol (#), while multi-line comments can be enclosed between /* and */. Comments are essential for leaving notes, explaining code, or temporarily disabling blocks of code. They are ignored by the PHP interpreter, making them purely informational for developers. Learn more: https://www.php.net/manual/en/language.basic-syntax.comments.php

The json_decode() function in PHP is used to decode a JSON object into a PHP array. It is a standalone function that takes a JSON-encoded string and converts it into a PHP value, typically an array or an object. The correct option is "function." For more information, consult the PHP documentation on json_decode(): http://php.net/manual/en/function.json-decode.php

The method seek() of the RandomAccessFile class in Java is used to set the file-pointer offset to a specified location within the file. It allows you to navigate within the file and start reading or writing data from that position.

In Java, you can use the static valueOf method of the Integer class to obtain a string representation of a primitive data type. For example, Integer.valueOf(42) will return the string "42". The other options do not provide this specific functionality.

Merge Sort has a space complexity of O(n) because it creates a temporary array to hold the merged subarrays during the sorting process. Unlike some other sorting algorithms like Quick Sort, Merge Sort does not use a constant amount of extra memory (O(1)) or divide the memory usage logarithmically (O(log n)).

The Serializable interface in Java does not contain any methods. Instead, it serves as a marker interface, indicating that the class implementing it can be serialized. Serialization allows objects to be converted into a byte stream for storage or transmission. It's used for objects that need to be saved to a file or sent over a network.