autocloseable

How does the try-with feature work for AutoCloseable variables that have been declared null ? I assumed this would lead to a null pointer exception when it attempts to invoke close on the variable, but it runs no problem: try (BufferedReader br = null){ System.out.println("Test"); } catch (IOException e){ e.printStackTrace(); } The Java Language Specification specifies that it is closed only if non-null, in section 14.20.3. try-with-resources : A resource is closed only if it initialized to a non-null value. This can actually be useful, when a resource might present sometimes, and absent

I read that the catch block in try-with-resources is optional. I've tried creating a Connection object in a try-with-resources block, with no subsequent catch block, only to get compiler error from eclipse: "Unhandled exception type SQLException thrown by automatic close() invocation." Since every resource that can be used in try-with-resources implements AutoCloseable , and so potentially throws an exception upon invocation of the close() method, I don't understand how the catch clause is optional, given that it's not allowing me to skip catching the exception from close() . Is there some

In C#, it is considered bad practice to throw exceptions in the Dispose method of an IDisposable . By contrast, in java the close method of AutoCloseable allows any Exception whatsoever to be thrown and forces the caller to handle it somehow. But what is the caller reasonably expected to do if this happens? This suggests that the attempt to close the resource failed somehow. So does the user have to try to close the resource again before continuing, perhaps with some sort of exponential backoff? It looks like every operation involving the resources, including the implicit close() invocation,

Kotlin provides the use function for Closeable objects, but it seems they forgot to consider AutoCloseable (e.g. DB prepared statements) for the try-with-resources full Java equivalent. I've implemented the next "home-made" solution: inline fun <T:AutoCloseable,R> trywr(closeable: T, block: (T) -> R): R { try { return block(closeable); } finally { closeable.close() } } Then you can use it the next way: fun countEvents(sc: EventSearchCriteria?): Long { return trywr(connection.prepareStatement("SELECT COUNT(*) FROM event")) { var rs = it.executeQuery() rs.next() rs.getLong(1) } } I'm new to

This question already has an answer here: Close multiple resources with AutoCloseable (try-with-resources) 4 answers I am new in Java8 , and I want to know if, for the AutoCloseable resource, I have to add a try for each resource , or it will work with the code above try (Connection conn = getConnection();) { Statement stmt = conn.createStatement(); ResultSet rset = stmt.executeQuery(sql); while (rset.next()) { TelefonicaDataVO vo = new TelefonicaDataVO(); vo.setTelefonicaDataId(rset.getString("Telefonica_PSD_ID")); vo.setReceptionDate(nvl(rset.getTimestamp("CREATION_DATE"))); vo.setMessage

Java docs of close() method of java.lang.AutoCloseable says Note that unlike the close() method of Closeable , this close() method is not required to be idempotent . In other words, calling this close method more than once may have some visible side effect, unlike Closeable#close() which is required to have no effect if called more than once. However, implementers of this interface are strongly encouraged to make their close methods idempotent. What do they mean by idempotent method and what are the side effects of calling this close() method twice? And since interface Closeable extends