How Programmer Handle an Exception?
Customized Exception Handling: Java exception handling is managed via five keywords: try, catch, throw, throws, and finally. Briefly, here is how they work. Program statements that you think can raise exceptions are contained within a try block. If an exception occurs within the try block, it is thrown. Your code can catch this exception (using catch block) and handle it in some rational manner. System-generated exceptions are automatically thrown by the Java run-time system. To manually throw an exception, use the keyword throw. Any exception that is thrown out of a method must be specified as such by a throws clause. Any code that absolutely must be executed after a try block completes is put in a finally block.
Tip: One must go through control flow in try catch finally block for better understanding.
Need for try-catch clause(Customized Exception Handling)
Consider the below program in order to get a better understanding of the try-catch clause.
Example:
Java
// Java Program to Demonstrate // Need of try-catch Clause // Class class GFG { // Main driver method public static void main(String[] args) { // Taking an array of size 4 int[] arr = new int[4]; // Now this statement will cause an exception int i = arr[4]; // This statement will never execute // as above we caught with an exception System.out.println("Hi, I want to execute"); } } |
Output
Output explanation: In the above example, an array is defined with size i.e. you can access elements only from index 0 to 3. But you trying to access the elements at index 4(by mistake) that’s why it is throwing an exception. In this case, JVM terminates the program abnormally. The statement System.out.println(“Hi, I want to execute”); will never execute. To execute it, we must handle the exception using try-catch. Hence to continue the normal flow of the program, we need a try-catch clause.
How to Use the Try-catch Clause?
try {
// block of code to monitor for errors
// the code you think can raise an exception
} catch (ExceptionType1 exOb) {
// exception handler for ExceptionType1
} catch (ExceptionType2 exOb) {
// exception handler for ExceptionType2
}
// optional
finally { // block of code to be executed after try block ends
}
Certain key points need to be remembered that are as follows:
- In a method, there can be more than one statement that might throw an exception, So put all these statements within their own try block and provide a separate exception handler within their own catch block for each of them.
- If an exception occurs within the try block, that exception is handled by the exception handler associated with it. To associate the exception handler, we must put a catch block after it. There can be more than one exception handler. Each catch block is an exception handler that handles the exception to the type indicated by its argument. The argument, ExceptionType declares the type of exception that it can handle and must be the name of the class that inherits from the Throwable class.
- For each try block, there can be zero or more catch blocks, but only one final block.
- The finally block is optional. It always gets executed whether an exception occurred in try block or not. If an exception occurs, then it will be executed after try and catch blocks. And if an exception does not occur, then it will be executed after the try block. The finally block in Java is used to put important codes such as clean-up code e.g., closing the file or closing the connection.
- If we write System.exit in the try block, then finally block will not be executed.
The summary is depicted via visual aid below as follows:
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