The catch Blocks
You associate exception handlers with a try block by providing one or more catch blocks directly after the try block. No code can be between the end of the try block and the beginning of the first catch block.
try < >catch (ExceptionType name) < >catch (ExceptionType name)
Each catch block is an exception handler that handles the type of exception indicated by its argument. The argument type, ExceptionType , declares the type of exception that the handler can handle and must be the name of a class that inherits from the Throwable class. The handler can refer to the exception with name .
The catch block contains code that is executed if and when the exception handler is invoked. The runtime system invokes the exception handler when the handler is the first one in the call stack whose ExceptionType matches the type of the exception thrown. The system considers it a match if the thrown object can legally be assigned to the exception handler’s argument.
The following are two exception handlers for the writeList method:
try < >catch (IndexOutOfBoundsException e) < System.err.println("IndexOutOfBoundsException: " + e.getMessage()); >catch (IOException e)
Exception handlers can do more than just print error messages or halt the program. They can do error recovery, prompt the user to make a decision, or propagate the error up to a higher-level handler using chained exceptions, as described in the Chained Exceptions section.
Catching More Than One Type of Exception with One Exception Handler
In Java SE 7 and later, a single catch block can handle more than one type of exception. This feature can reduce code duplication and lessen the temptation to catch an overly broad exception.
In the catch clause, specify the types of exceptions that block can handle, and separate each exception type with a vertical bar ( | ):
catch (IOException|SQLException ex)
Note: If a catch block handles more than one exception type, then the catch parameter is implicitly final . In this example, the catch parameter ex is final and therefore you cannot assign any values to it within the catch block.
Catch exception java list
правильно ли понимаю, что когда я работаю с проектом, в котором есть несколько потоков исполнения, может быть вот такая ситуация. Один из этих потоков запускается и завершается успешно, а затем выбрасывает исключение внутри блока try-catch. Оставшиеся потоки исполнения продолжают свою работу, но никакой код в блоке finally не выполняется. Тогда блок finally при обработке исключений не будет выполнен?
я читаю про исключения на 1м и в принципе понимаю, но не очень. ps: зачем только я начал с java core. pss: если вы это читаете, и я до сих пор на первом, то либо я прохожу другой курс, либо читаю книгу по джаве, параллельно проходя этот курс, либо решил взять перерыв на неопределенный срок времени. никогда не сдамся)
Есть подозрение, что так будет правильнее.
обращу внимание на некоторую неточность. цитата «Создание исключения При исполнении программы исключение генерируется JVM или вручную, с помощью оператора throw» в java исключения это тоже объекты поэтому создается исключение так же как объект new Exception. а бросается в программе с помощью оператора throw. обычно эти операции объединяют в одну throw new Exception(«aaa»);
если что я пишу это с 3 уровня. Под конец лекций я читал статью про бафридер, после нашел там ссылку на потоки вводов, а потом чтобы понять что там говориться ввел гугл про исключение и нашел эту статью, спасибо автору, это статья очень помогла. PS если ты читаешь этот комментарий и видишь что у меня нет прогресса(то есть если я все еще на 3 уровне или чуточку больше), то скажи мне, что я нуб и не дошел до 40 лвла
Catching Multiple Exception Types and Rethrowing Exceptions with Improved Type Checking
In Java SE 7 and later, a single catch block can handle more than one type of exception. This feature can reduce code duplication and lessen the temptation to catch an overly broad exception.
Consider the following example, which contains duplicate code in each of the catch blocks:
catch (IOException ex) < logger.log(ex); throw ex; >catch (SQLException ex)
In releases prior to Java SE 7, it is difficult to create a common method to eliminate the duplicated code because the variable ex has different types.
The following example, which is valid in Java SE 7 and later, eliminates the duplicated code:
catch (IOException|SQLException ex)
The catch clause specifies the types of exceptions that the block can handle, and each exception type is separated with a vertical bar ( | ).
Note: If a catch block handles more than one exception type, then the catch parameter is implicitly final . In this example, the catch parameter ex is final and therefore you cannot assign any values to it within the catch block.
Bytecode generated by compiling a catch block that handles multiple exception types will be smaller (and thus superior) than compiling many catch blocks that handle only one exception type each. A catch block that handles multiple exception types creates no duplication in the bytecode generated by the compiler; the bytecode has no replication of exception handlers.
Rethrowing Exceptions with More Inclusive Type Checking
The Java SE 7 compiler performs more precise analysis of rethrown exceptions than earlier releases of Java SE. This enables you to specify more specific exception types in the throws clause of a method declaration.
Consider the following example:
static class FirstException extends Exception < >static class SecondException extends Exception < >public void rethrowException(String exceptionName) throws Exception < try < if (exceptionName.equals("First")) < throw new FirstException(); >else < throw new SecondException(); >> catch (Exception e) < throw e; >> This examples’s try block could throw either FirstException or SecondException . Suppose you want to specify these exception types in the throws clause of the rethrowException method declaration. In releases prior to Java SE 7, you cannot do so. Because the exception parameter of the catch clause, e , is type Exception , and the catch block rethrows the exception parameter e , you can only specify the exception type Exception in the throws clause of the rethrowException method declaration.
However, in Java SE 7, you can specify the exception types FirstException and SecondException in the throws clause in the rethrowException method declaration. The Java SE 7 compiler can determine that the exception thrown by the statement throw e must have come from the try block, and the only exceptions thrown by the try block can be FirstException and SecondException . Even though the exception parameter of the catch clause, e , is type Exception , the compiler can determine that it is an instance of either FirstException or SecondException :
public void rethrowException(String exceptionName) throws FirstException, SecondException < try < // . >catch (Exception e) < throw e; >>
This analysis is disabled if the catch parameter is assigned to another value in the catch block. However, if the catch parameter is assigned to another value, you must specify the exception type Exception in the throws clause of the method declaration.
In detail, in Java SE 7 and later, when you declare one or more exception types in a catch clause, and rethrow the exception handled by this catch block, the compiler verifies that the type of the rethrown exception meets the following conditions:
- The try block is able to throw it.
- There are no other preceding catch blocks that can handle it.
- It is a subtype or supertype of one of the catch clause’s exception parameters.
The Java SE 7 compiler allows you to specify the exception types FirstException and SecondException in the throws clause in the rethrowException method declaration because you can rethrow an exception that is a supertype of any of the types declared in the throws .
In releases prior to Java SE 7, you cannot throw an exception that is a supertype of one of the catch clause’s exception parameters. A compiler from a release prior to Java SE 7 generates the error, «unreported exception Exception ; must be caught or declared to be thrown» at the statement throw e . The compiler checks if the type of the exception thrown is assignable to any of the types declared in the throws clause of the rethrowException method declaration. However, the type of the catch parameter e is Exception , which is a supertype, not a subtype, of FirstException and SecondException . catch parameter, and the exception handled by this catch block is not reassigned, then these exception types are implicitly final . You may explicitly declare these exception types as final ; however this is not necessary:
catch (final IOException|SQLException ex)
Exception types that are not final (in particular, catch blocks in which the handled exception is reassigned) affect the features discussed on this page as follows:
- The compiler generates an error for catch blocks that handles more than one exception type.
- The compiler will not perform the more inclusive type checking for rethrown exceptions.