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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).
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Can you throw exception from catch block?
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.
Can NullPointerException be used with ArithmaticException using throws keyword in java?
No. You cannot throw or catch Null pointer exceptions
Why use throw in java in compare try-catch?
we use throws in our program so that we dont need to write try & catch block & to avoid the exception
How do you throw exception in java?
we do it using the throw keyword.
When should we use exception handling in java?
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.
What is throw keyword in java?
The throw keyword is used from within a method to "throw" an exception to the calling method. In order to throw an exception, the method signature must indicate that it will throw an exception. For example: public void foo() throws Exception { } When you want to actually throw the exception, you can do it a few different ways: throw new Exception("Exception message"); or from within a catch block ( catch(Exception ex) ): throw ex;
How do you say I like to throw and catch a football?
I say it this way: "I like to throw and catch a football."
Throws statement in java?
throw new Throwable(); or throw new Error("Danger will Robinson!"); or throw new NullPointerException(); etc.
What is the antonym to catch?
An antonym of catch is pitch or throw.
What can you throw but catch?
Cold.
What is exception and give a simple example in java programming?
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
What can you do with a Frisbee?
you can throw it, play catch with it, be mean and throw it at ppl. ETC...
