Exception Handling in Java

Automation Testing Interview Help, Java, Test Automation / April 21, 2021 April 21, 2021 / 225 Comments

An exception is nothing but an unwanted or unexpected event that occurs during the execution of a program. In such case, normal flow of the program is disturbed, and program terminates abnormally, which is not a good practice, therefore there is a need to handle these exceptions. Exception handling is a mechanism to handle runtime exceptions in order to maintain execution of a program without any interruption.

Advantage of exception handling

The main advantage of exception handling is to maintain the normal flow of the application.

Let’s consider following scenario:

{
1.	Statement 1;
2.	Statement 2;
3.	Statement 3; // Suppose exception occurs at this line
4.	Statement 4;
5.	Statement 5;
}

In this scenario, there are 5 statements and exception occur at statement 3, the rest of the code will not be executed meaning statement 4 and statement 5 will not be executed. If we implement exception handling, the rest of the statements will be executed.

Exception Hierarchy

Types of Java Exceptions:

Checked Exception

Checked exceptions are checked at compile-time. If some method throws a checked exception, then the method must either handle the exception or it must specify the exception using throws keyword.

Example: Consider below program which throws checked exception.

** Above Java program opens a file at location “C:\Exception-Handling\a.txt” and prints all lines of it. The program doesn’t compile, because the function main() uses FileReader() and FileReader() throws a checked exception FileNotFoundException. It also uses readLine() and close() methods, and these methods also throw checked exception IOException

There are two ways to handle checked exception

1. Use throws keyword to declare checked exception

Since FileNotFoundException is a subclass of IOException, we can just specify IOException in the throws list.

2. Use try-catch block

Unchecked Exception

Unchecked exceptions are not checked at compile-time, but they are checked at runtime. If a program throws an unchecked exception, it means there is some error in the program logic.

we don’t have to declare unchecked exceptions in a method with the throws keyword. And although the above code does not have any errors during compile-time, it will throw ArithmeticException at runtime.

Errors

Errors are the problems which are irrecoverable. These problems are beyond the control of the programmer, these are not exceptions. Errors are typically ignored in the code because we can rarely do anything about an error.

Java Exception Keywords

try:

Exception prone code can be placed in a block specified by “try” keyword. The try block must be followed by either catch or finally. We cannot use try block alone.

catch:

The exception can be handled by “catch” block. It must be preceded by try block which means we cannot use catch block alone. It can be followed by finally block later.

Syntax of java try-catch block:

try {    
   //code that may throw an exception    
}
 catch(Exception_class_Name ref){}

Example:

finally:

The “finally” block always executes, irrespective of occurrence of an exception. This block follows a try block or a catch block.

Syntax of try-finally block:

try{    
   //code that may throw an exception    
}
finally{}

Example:

Output:

Syntax of try-catch-finally block:

Output:

‘throw’ keyword in Java

The “throw” keyword is used to throw an exception from any block of code or a method. This exception can be checked or unchecked.

Syntax:

throw exception

Example:

‘throws’ declaration in Java

The “throws” keyword is used to declare exceptions. It does not throw an exception. It specifies that there may occur an exception in the method. It is always used with method signature.