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The statements within the try block are executed, and if any of them throws an exception, execution of the block is discontinued and the exception is handled by the catch block. There may be multiple catch blocks, in which case the first block with an exception variable whose type matches the type of the thrown exception is executed.
try {// Normal execution path. throw new EmptyStackException ();} catch (ExampleException ee) {// Deal with the ExampleException.} finally {// Always run when leaving the try block (including finally clauses), regardless of whether any exceptions were thrown or whether they were handled. // Cleans up and closes resources acquired in the try block.
Also common is a related clause (finally or ensure) that is executed whether an exception occurred or not, typically to release resources acquired within the body of the exception-handling block. Notably, C++ does not provide this construct, recommending instead the Resource Acquisition Is Initialization (RAII) technique which frees resources ...
In Object Pascal, D, Java, C#, and Python a finally clause can be added to the try construct. No matter how control leaves the try the code inside the finally clause is guaranteed to execute. This is useful when writing code that must relinquish an expensive resource (such as an opened file or a database connection) when finished processing:
Social pressure is a major influence on the scope of exceptions and use of exception-handling mechanisms, i.e. "examples of use, typically found in core libraries, and code examples in technical books, magazine articles, and online discussion forums, and in an organization’s code standards". [10]
Functionality like these "finally" clauses can be implemented by a goto to the single return point of the subroutine. An alternative solution is to use the normal stack unwinding (variable deallocation) at function exit to unallocate resources, such as via destructors on local variables, or similar mechanisms such as Python's "with" statement.
C# makes use of reification to provide "first-class" generic objects that can be used like any other class, with code generation performed at class-load time. [29] Furthermore, C# has added several major features to accommodate functional-style programming, culminating in the LINQ extensions released with C# 3.0 and its supporting framework of ...
A common reason for using try-finally blocks is to guard resource managing code, thus guaranteeing the release of precious resources in the finally block. C# features the using statement as a syntactic shorthand for this common scenario, in which the Dispose() method of the object of the using is always called.