Exception handling if done by
1)Error detection
2)Error Reporting
3)Error Handling
Is implemented by following keywordstry,catch,finally,throws,throws
try{}
If exception occurs in try block the appropriate exception handlers that is associated with the try block handles the exception.
try block must have atleast one catch block follows it immediately
catch(Exception e){}
The catch statement take object of an exception as parameter .
If an exception is thrown the statements in the catch block is executed.
There should not be any statement between try and catch block.
we can have more then one catch block for one try block.
finally{}
It not mandatory to have a finally block
Sometime it is necessary to process certain statement whether exception occur or not
finally block exceutes even if exception occurs or not
Other then try catch block we directly handle a exception by using throws keywordthrow keyword allows us to create user define exception
Yes. Exception handling allows developers to detect errors easily without writing special code to test return values. Even better, it lets us keep exception-handling code cleanly separated from the exception-generating code. It also lets us use the same exception-handling code to deal with a range of possible exceptions.
Exception handling works by transferring the execution of a program to an appropriate exception handler when an exception occurs. For ex: Your website displays the users bank account details. Suddenly if the bank database is down, imaging how the user would feel if an abrupt error page with numerous lines of java exception messages spewed all over the screen? First of all, it would be embarrassing and second of all, the user will get annoyed. Instead, if your code catches this database down scenario and displays a graceful message on screen saying "We are currently experiencing some difficulties in our system. Kindly try after some time. Thank you" it would be much better isn't it? That is exactly why we have or rather why we need Exception Handling.
The term "exception" means "exceptional condition" and is an occurrence that alters the normal program flow. A bunch of things can lead to exceptions, including hardware failures, resource exhaustion, and good old bugs. When an exceptional event occurs in Java, an exception is said to be "thrown." The code that's responsible for doing something about the exception is called an "exception handler," and it "catches and handles" the thrown exception.
Exception handling works by transferring the execution of a program to an appropriate exception handler when an exception occurs. For ex: Your website displays the users bank account details. Suddenly if the bank database is down, imaging how the user would feel if an abrupt error page with numerous lines of java exception messages spewed all over the screen? First of all, it would be embarrassing and second of all, the user will get annoyed. Instead, if your code catches this database down scenario and displays a graceful message on screen saying "We are currently experiencing some difficulties in our system. Kindly try after some time. Thank you" it would be much better isnt it? That is exactly why we have or rather why we need Exception Handling.
To do this, we use the try and catch keywords. The try is used to define a block of code in which exceptions may occur. This block of code is called a guarded region (which really means "risky code goes here"). One or more catch clauses match a specific exception to a block of code that handles it. Here's how it looks in pseudocode:
1. try {
2. // This is the "guarded region"
3. // All your bank database access code goes here
4. // And any other code that might process that data
5. // We may have many code lines here
6. }
7. catch(DatabaseDownException) {
8. // Put code here that handles this exception.
9. // Put the graceful error message here
10. // This is the last line of the exception handler.
11. }
12. catch(SomeOtherException) {
13. // Put code here that handles this exception
14. }
15.
16. // Some other unguarded code continues from here
In this pseudocode example, lines 2 through 5 constitute the guarded region that is governed by the try clause. Line 7 is an exception handler for an exception of type DatabaseDownException. Line 12 is an exception handler for an exception of type SomeOtherException. Notice that the catch blocks immediately follow the try block. This is a requirement; if you have one or more catch blocks, they must immediately follow the try block. Additionally, the catch blocks must all follow each other, without any other statements or blocks in between. Also, the order in which the catch blocks appear matters. For now just know this. We will see more in detail about their order a little bit later.
Execution of the guarded region starts at line 2. If the program executes all the way past line 5 with no exceptions being thrown, execution will transfer to line 15 and continue downward. However, if at any time in lines 2 through 5 (the try block) an exception is thrown of type DatabaseDownException, execution will immediately transfer to line 7. Lines 8 through 10 will then be executed so that the entire catch block runs, and then execution will transfer to line 15 and continue.
Note that if an exception occurred on, say, line 3 of the try block, the rest of the lines in the try block (4 and 5) would never be executed. Once control jumps to the catch block, it never returns to complete the balance of the try block. This is exactly what you want, though. Imagine your code looks something like this pseudocode:
try {
getTheFileFromOverNetwork
readFromTheFileAndPopulateTable
}
catch(CantGetFileFromNetwork) {
displayNetworkErrorMessage
}
The preceding pseudocode demonstrates how you typically work with exceptions. Code that's dependent on a risky operation (as populating a table with file data is dependent on getting the file from the network) is grouped into a try block in such a way that if, say, the first operation fails, you won't continue trying to run other code that's also guaranteed to fail. In the pseudocode example, you won't be able to read from the file if you can't get the file off the network in the first place.
One of the benefits of using exception handling is that code to handle any particular exception that may occur in the governed region needs to be written only once. Returning to our earlier code example, there may be three different places in our try block that can generate a DatabaseDownException, but wherever it occurs it will be handled by the same catch block (on line 7).
In Java there are two main types of Exceptions. * Checked Exceptions - The ones that can be checked & handled in our code. Ex: I/O Exception, SQL Exception etc. In most cases, the compiler itself forces us to catch & handle these exceptions * Un-checked Exceptions - The ones that we cannot & should not handle in our code. Ex. Null Pointer Exception The java.lang.Throwable is the super class of all errors and exceptions in Java. Only objects of this class can be thrown & caught and handled by try-catch blocks. Ex: try { ..... ..... } catch (Exception e){ ... } finally { ... }
In Java, Exception Handling is Explicit. The Programmer has to write code that will ensure that the exceptions are caught and appropriately handled
though catching exceptions is a good practice inside java code, catching all exceptions of the type exception is not the best way to go. Specific exceptions need to be caught instead of the generic Exception being caught. Also, different types of exceptions need to be handled separately.
In Java, errors that arise during the execution of the program are more formally referred to as Exceptions. Exceptions can be handled using try catch blocks. Here is an example : try { int answer = 42 / 0 ; } catch ( ArithmeticException e ) { e.printStackTrace(); }
it informs compiler about its possible exceptions. For example,The purpose of Java exception is to tell the Java runtime system what can go wrong
In Java there are two main types of Exceptions. * Checked Exceptions - The ones that can be checked & handled in our code. Ex: I/O Exception, SQL Exception etc. In most cases, the compiler itself forces us to catch & handle these exceptions * Un-checked Exceptions - The ones that we cannot & should not handle in our code. Ex. Null Pointer Exception The java.lang.Throwable is the super class of all errors and exceptions in Java. Only objects of this class can be thrown & caught and handled by try-catch blocks. Ex: try { ..... ..... } catch (Exception e){ ... } finally { ... }
In Java, Exception Handling is Explicit. The Programmer has to write code that will ensure that the exceptions are caught and appropriately handled
though catching exceptions is a good practice inside java code, catching all exceptions of the type exception is not the best way to go. Specific exceptions need to be caught instead of the generic Exception being caught. Also, different types of exceptions need to be handled separately.
Exceptions are of two types: checked exceptions and unchecked exceptions.
In Java, errors that arise during the execution of the program are more formally referred to as Exceptions. Exceptions can be handled using try catch blocks. Here is an example : try { int answer = 42 / 0 ; } catch ( ArithmeticException e ) { e.printStackTrace(); }
it informs compiler about its possible exceptions. For example,The purpose of Java exception is to tell the Java runtime system what can go wrong
The try keyword is used in Java to handle problematic situations that are commonly known as "Exceptions" The try keyword is used in conjunction with the catch keyword. If any exception is thrown by code inside the try block, they will be caught and handled by the catch block. Ex: try { ... ... } catch (Exception e){ ... }
Checked exceptions are exceptions which need to be handled explicitly. These are the ones which require a try-catchblock or a throws keyword.Unchecked exceptions are exceptions which have no obligation to be handled. A NullPointerException is one common example.
To handle the exceptions in large programs
Exception is a situation in Java wherein the system is behaving in a not-so-correct way or rather the system is behaving in an erroneous way. Exceptions are handled using try-catch blocks. Ex: try { int x = 10/0; } catch (Exception e) { e.printStackTrace(); } Here we are performing an illegal operation by dividing 10/0 which will throw a numeric exception which will be caught and handled inside the catch block
Exception handling is largely the same for both. The only real difference is that C++ has no 'finally' clause which always executes whether an exception occurs or not. Another difference is that Java throws exceptions and errors, but errors cannot be handled since programs cannot handle errors -- such as the JVM out of memory error.
Only instances of subclasses of throwable can be used in conjunction with the throw keyword. In java all exceptions and errors are subclasses of throwable.