These are the times that try men's souls.
Thomas Paine, The American Crisis (1780)
. . . and they all fell to playing the game of catch as catch can,
till the gunpowder ran out at the heels of their boots.
Samuel Foote
A try
statement executes a block. If a value is thrown and the try
statement has
one or more catch
clauses that can catch it, then control will be transferred to the
first such catch
clause. If the try
statement has a finally
clause, then another
block of code is executed, no matter whether the try
block completes normally or
abruptly, and no matter whether a catch
clause is first given control.
TryStatement:
try
BlockCatches
try
BlockCatchesopt
Finally Catches:
CatchClause
CatchesCatchClause CatchClause:
catch (
FormalParameter)
Block Finally:
finally
Block
The following is repeated from §8.4.1 to make the presentation here clearer:
FormalParameter:
TypeVariableDeclaratorId
The following is repeated from §8.3 to make the presentation here clearer:
VariableDeclaratorId:
Identifier
VariableDeclaratorId[ ]
The Block immediately after the keyword try
is called the try
block of the try
statement. The Block immediately after the keyword finally
is called the finally
block of the try
statement.
A try
statement may have catch
clauses (also called exception handlers). A catch
clause must have exactly one parameter (which is called an exception parameter); the declared type of the exception parameter must be the class Throwable
or a subclass of Throwable
, or a compile-time error occurs. The scope of the parameter variable is the Block of the catch
clause. An exception parameter must not have the same name as a local variable or parameter in whose scope it is declared, or a compile-time error occurs.
The scope of the name of an exception parameter is the Block of the catch
clause. The name of the parameter may not be redeclared as a local variable or exception parameter within the Block of the catch
clause; that is, hiding the name of an exception parameter is not permitted.
Exception parameters cannot be referred to using qualified names (§6.6), only by simple names.
Exception handlers are considered in left-to-right order: the earliest possible catch
clause accepts the exception, receiving as its actual argument the thrown exception object.
A finally
clause ensures that the finally
block is executed after the try
block and any catch
block that might be executed, no matter how control leaves the try
block or catch
block.
Handling of the finally
block is rather complex, so the two cases of a try
statement with and without a finally
block are described separately.