Hibernate ORM and Unix/Linux Programming Quiz

The sed command sed 's/[ ][^ ]*$//' matches a space followed by any non-space characters at the end of a line and removes them, effectively stripping trailing spaces from each line of the file.

dup() is the POSIX system call used to duplicate file descriptors. It creates a new file descriptor that refers to the same open file description as the original, sharing the file offset and status flags. dup2() is a related call that allows specifying the descriptor number. cp() is for file copying, mknod() creates device nodes.

at and cron are both Unix job scheduling utilities. at schedules one-time jobs and takes input directly from the user (stdin), while cron schedules recurring jobs by reading configuration from crontab files.

lprm is the standard Unix/Linux command for removing jobs from the printer queue. lpqrm does not exist, jobs -r is for shell jobs, and lpc -rm is not the correct syntax.

Restarting the inet service (internet super-server) does NOT close existing open sockets. The service restarts but established connections remain active until properly closed by the applications using them.

telnet uses a byte-oriented protocol and was designed specifically for terminal emulation, while rsh (remote shell) uses a stream protocol for executing commands on remote hosts. Their underlying communication protocols differ.

In Hibernate, evict() removes an object and its associated collections from the first-level cache (session cache). This detaches the object from the session, making changes no longer tracked. It does NOT affect second-level cache or the database.

Traditional Unix shell scripting (sh, bash) does not natively support floating-point arithmetic. Operations like 1.5 + 2.3 require external tools like bc, awk, or zsh's floating-point support. Only integer arithmetic is built-in.

The system() function in C/C++ executes a shell command and returns an implementation-defined value that can be processed. Typically, it returns the exit status of the command (or 0 on success, -1 if fork fails, or another value if the shell could not be executed). Programmers routinely check this return value to determine if the command succeeded or failed, making it processable.

In Hibernate, the Session object is explicitly NOT thread-safe and is designed for use by a single thread at a time. Hibernate's documentation states that sharing a Session across threads without synchronization can cause unpredictable behavior. For concurrent access, you should use separate Session instances per thread or consider using Hibernate's SessionFactory with proper isolation. Each thread should obtain its own Session from the SessionFactory.

The lpc (line printer control) command is a Unix/Linux utility used to manage print jobs and printer queues. It allows administrators to perform operations like starting and stopping printers, enabling and disabling queues, rearranging print jobs, and checking queue status. Option A correctly identifies its primary purpose. Options B and C are incorrect because lpc works with printers and queues, not modems or flash drives. Option D is wrong because lpc is a valid, widely-used command.

In Hibernate, making a property read-only from the application side (while still loading it from the database) is achieved by setting insert="false" and update="false" in the mapping XML or annotations. This tells Hibernate to retrieve the property value when loading objects but never include it in INSERT or UPDATE statements. Option A correctly states this. Options B and C use incorrect attribute names (should be 'insert' and 'update', not 'isinsert' and 'isupdate'), making them invalid.

In Unix-like operating systems, the kill() system call is used to send a signal to a process or a group of processes, despite its name suggesting it only terminates them.

In Hibernate, a Session is lightweight and does not immediately acquire a JDBC connection from the connection pool or datasource upon creation. It only obtains a connection when a database transaction or query requires it.

To enable query cache in Hibernate, you set the property hibernate.cache.use_query_cache to true (not 'yes' or without the 'use_' prefix). This property, along with configuring a second-level cache provider, enables caching of query result sets. Option B correctly states the property name and value. Options A and C are incorrect because they use 'query_cache' instead of 'use_query_cache'. Option D is wrong because query cache can be enabled with the correct property.

Session.get() is the better choice when you're uncertain whether a row exists. The get() method returns null if no matching row is found, allowing you to handle the absence gracefully. In contrast, Session.load() assumes the row exists and throws an ObjectNotFoundException if it doesn't, which would cause an uncaught exception in your code. Option B is correct. Options C and D are incorrect because there's no Session.fetch() method in standard Hibernate, and load() would cause an exception.

To solve this question, the user needs to have knowledge about the concept of a bag data structure. A bag is a collection of unordered elements that may contain duplicates.

Now, let's go through each option and explain why it is right or wrong:

a) bag has index column: This statement is incorrect. A bag is an unordered collection, which means it does not have an index column. Items in a bag are stored in any order.

b) bag permits duplicate element values: This statement is correct. A bag allows duplicate elements to be added to it. For example, a bag can contain two or more items with the same value.

c) bag does not permit duplicate element values: This statement is incorrect. A bag permits duplicate elements to be added to it. Therefore, this statement is false.

d) None: This option is incorrect because option B is correct.

The Answer is: B

The refresh() method re-loads an object and all its collections from the database, overwriting the current state in the Session. This is particularly useful when database triggers initialize or modify properties after the initial save - refresh() retrieves those trigger-generated values. Option A correctly identifies refresh(). Option B (flush) synchronizes the Session state to the database (writes to DB, not reads from it). Options C and D are incorrect because there's no standard fetch() method, and load() retrieves only if already in Session or throws exception.

is the root element in hibernate.cfg.xml (Hibernate's main configuration file). Individual mapping files use , but is a child element, not the root.