class CatchException
{ public static void main(String args[])
{
try
{
int j=45/0;
}catch(Exception exp){System.out.println("Exception caught "+exp.stacktrace());}
}
}
Catching Exceptions - Using try and catch
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 isn't 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).
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.
Catching Exceptions - Using try and catch
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 isn't 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).
You catch exceptions in java using the try - catch block in Java.
Whenever the code inside a try block throws an exception the catch block would catch and process it gracefully instead of the application terminating abruptly.
Example:
try {
.....
int x = 100/0; //This would throw an ArithmeticException
....
} catch (ArithmeticException e){
//handle the exception here...
} catch (Exception ex){
//Adding the exception catch here so that any other exception thrown would also be handled gracefully
}
Always the catch (Exception e) should be last catch block. the child exceptions should be caught first and then the parent exceptions.
If we have it the other way round we would get unreachable code block error during compilation.
Do some reading on try ... catch. The Java documentation at the Oracle site includes some examples.
no, because catch is used to handle exceptions which are generated from try block
Here is a code snippet illustrating exception handling: try { int a= 3 / 0 ; } catch ( ArithmeticException e ) { System.out.println ("An ArithmeticException has occured"); } finally { // some code }
We can create a exception sub class by extending Exception class available in java
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, if there is a run-time error then it allows the user to explicitly handle it by catching it in the catch block. If there is any error in the try block of code, automatically the flow control will be transferred to the catch block. Here Exception e indicates any exception. The same is true in both Visual Basic and C#. This is seen in the try {} catch (Exception e) {} blocks. Which then function as the previous poster said. == == == ==
no, because catch is used to handle exceptions which are generated from try block
A Catch block is part of the exception handling mechanism in Java. It is used along with the try block. Ex: try { ... } catch (Exception e) { ... } The catch block is used to catch & handle the exception that gets thrown in the try block.
Here is a code snippet illustrating exception handling: try { int a= 3 / 0 ; } catch ( ArithmeticException e ) { System.out.println ("An ArithmeticException has occured"); } finally { // some code }
Exception handling should be used in Java in all cases where you as a programmer suspect that your code might throw some exceptions or create errors that might look ugly when a user is using the application. In such cases you use exception handling to catch and handle the exception and exit gracefully. You use the try - catch block in Java for exception handling.
We can create a exception sub class by extending Exception class available in java
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){ ... }
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 { ... }
100% yes but it is not a suggested practice. The purpose of a catch block in java code is to handle exceptions. If you want to throw exceptions, then there is no point in writing the try-catch block. We could throw the exception at the point where it occurs instead of writing the try - catch block to catch it and throw it again.
To handle the exceptions in large programs
the catch block catches the exception from the try block to display a proper message about the exception. Answered by, SOORAJ.M.S
It is called an exception. There are two ways of handling exceptions inside java methods. The method can have a try catch block and handle the error/exception inside the method. Or The method can throw the exception under the assumption that the calling method would have the code to handle the exception that is thrown by this method
In Java, if there is a run-time error then it allows the user to explicitly handle it by catching it in the catch block. If there is any error in the try block of code, automatically the flow control will be transferred to the catch block. Here Exception e indicates any exception. The same is true in both Visual Basic and C#. This is seen in the try {} catch (Exception e) {} blocks. Which then function as the previous poster said. == == == ==