24D. Java Basics for Selenium - Exception Handling - Interview Questions

Pubblicato il: 28 marzo 2019
sul canale di: subbus tech

In this video we will see some interview questions on exception handling.
What is an exception in java?
An exception is a run time error. In java exception is an object. Exceptions are created when an abnormal situations are arised in our program. Exceptions can be created by JVM or by our application code. All Exception classes are defined in java.lang.
State some situations where exceptions may arise in java?
1) Accessing an element that does not exist in array.
2) Dividing an integer by zero (Arithmeticexception)
2) Invalid conversion of number to string and string to number. (NumberFormatException)
3) Invalid casting of class (Class cast Exception)
4) Trying to create object for interface or abstract class (Instantiation Exception)
What is Exception handling in java?
Exception handling is a mechanism what to do when some abnormal situation arises in program. When an exception is raised in program it leads to termination of program when it is not handled properly. The significance of exception handling comes here in order not to terminate a program abruptly and to continue with the rest of program normally. This can be done with help of Exception handling.
In how many ways we can do exception handling in java?
We can handle exceptions in either of the two ways:
1) By specifying try catch block where we can catch the exception.
2) Declaring a method with throws clause.
List out five keywords related to Exception handling?
1) Try
2) Catch
3) throw
4) throws
5) finally
Explain try and catch keywords in java?
In try block we define all exception causing code. In java try and catch forms a unit. A catch block catches the exception thrown by preceding try block. Catch block cannot catch an exception thrown by another try block. If there is no exception causing code in our program or exception is not raised in our code jvm ignores the try catch block.
Syntax:
try {
}
Catch(Exception e) {
}
Can we have try block without catch block?
Each try block requires at least one catch block or finally block. A try block without catch or finally will result in compiler error. We can skip either of catch or finally block but not both.
Can we have multiple catch block for a try block?
In some cases our code may throw more than one exception. In such case we can specify two or more catch clauses, each catch handling different type of exception. When an exception is thrown jvm checks each catch statement in order and the first one which matches the type of exception is execution and remaining catch blocks are skipped.
Can we have any code between try and catch blocks?
We shouldn’t declare any code between try and catch block. Catch block should immediately start after try block.
Explain importance of finally block in java?
Finally, block is used for cleaning up of resources such as closing connections, sockets etc. if try block executes with no exceptions then finally is called after try block without executing catch block. If there is exception thrown in try block finally block executes immediately after catch block. If an exception is thrown, finally block will be executed even if the no catch block handles the exception.
Can we catch more than one exception in single catch block?
From Java 7, we can catch more than one exception with single catch block. This type of handling reduces the code duplication.
Note: When we catch more than one exception in single catch block , catch parameter is implicity final. We cannot assign any value to catch parameter.
Ex: catch(ArrayIndexOutOfBoundsException | ArithmeticException e) {
}
In the above example e is final we cannot assign any value or modify e in catch statement.
What are checked Exceptions?
1) All the subclasses of Throwable class except error, Runtime Exception and its subclasses are checked exceptions.
2) Checked exception should be thrown with keyword throws or should be provided try catch block, else the program would not compile.
We do get compilation error.
Examples:
1) IOException,
2) SQlException,
3) FileNotFoundException,
4) InvocationTargetException,
5) CloneNotSupportedException
6) ClassNotFoundException
7) InstantiationException
What are unchecked exceptions in java?
All subclasses of RuntimeException are called unchecked exceptions. These are unchecked exceptions because compiler does not checks if a method handles or throws exceptions. Program compiles even if we do not catch the exception or throws the exception. If an exception occurs in the program, program terminates. It is difficult to handle these exceptions because there may be many places causing exceptions.
Example :
1) Arithmetic Exception
3) ArrayIndexOutOfBoundsException
4) ClassCastException
5) IndexOutOfBoundException
6) NullPointerException
7) NumberFormatException
8) StringIndexOutOfBounds
9) UnsupportedOperationException

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