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In the Java programming language, the try...catch block is used often to catch exceptions. All potentially dangerous code is placed inside the block and, if an exception occurred, is stopped, or caught.
Catch ex As ExceptionType ' Handle Exception of a specified type (i.e. DivideByZeroException, OverflowException, etc.) Catch ex As Exception ' Handle Exception (catch all exceptions of a type not previously specified) Catch ' Handles anything that might be thrown, including non-CLR exceptions.
The scope for exception handlers starts with a marker clause (try or the language's block starter such as begin) and ends in the start of the first handler clause (catch, except, rescue). Several handler clauses can follow, and each can specify which exception types it handles and what name it uses for the exception object.
The first hardware exception handling was found in the UNIVAC I from 1951. Arithmetic overflow executed two instructions at address 0 which could transfer control or fix up the result. [16] Software exception handling developed in the 1960s and 1970s. Exception handling was subsequently widely adopted by many programming languages from the ...
Exception swallowing can also happen if the exception is handled and rethrown as a different exception, discarding the original exception and all its context. In this C# example, all exceptions are caught regardless of type, and a new generic exception is thrown, keeping only the message of the original exception.
IronPython allows running Python 2.7 programs (and an alpha, released in 2021, is also available for "Python 3.4, although features and behaviors from later versions may be included" [170]) on the .NET Common Language Runtime. [171] Jython compiles Python 2.7 to Java bytecode, allowing the use of the Java libraries from a Python program. [172]
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:
Try instructions Catch« name As exception»« When condition» instructions... «Finally instructions» End Try: System.Diagnostics.Debug.Assert(condition) or System.Diagnostics.Trace.Assert(condition) Xojo: Raise exception: Try instructions Catch «exception» instructions... «Finally instructions» End Try — Python: raise exception: try ...