Exception Handling

An exception is an unwanted or unexpected event, which occurs during the execution of a program i.e at run time, that disrupts the normal flow of the program’s instructions.

Error vs Exception

Error: An Error indicates serious problem that a reasonable application should not try to catch.
Exception: Exception indicates conditions that a reasonable application might try to catch.

next →← prev Exception Handling in Java Exception Handling Advantage of Exception Handling Hierarchy of Exception classes Types of Exception Exception Example Scenarios where an exception may occur The Exception Handling in Java is one of the powerful mechanism to handle the runtime errors so that normal flow of the application can be maintained. In this page, we will learn about Java exceptions, its type and the difference between checked and unchecked exceptions. What is Exception in Java Dictionary Meaning: Exception is an abnormal condition. In Java, an exception is an event that disrupts the normal flow of the program. It is an object which is thrown at runtime. What is Exception Handling Exception Handling is a mechanism to handle runtime errors such as ClassNotFoundException, IOException, SQLException, RemoteException, etc. Advantage of Exception Handling The core advantage of exception handling is to maintain the normal flow of the application. An exception normally disrupts the normal flow of the application that is why we use exception handling. Let's take a scenario: statement 1;   statement 2;   statement 3;   statement 4;   statement 5;//exception occurs   statement 6;   statement 7;   statement 8;   statement 9;   statement 10;   Suppose there are 10 statements in your program and there occurs an exception at statement 5, the rest of the code will not be executed i.e. statement 6 to 10 will not be executed. If we perform exception handling, the rest of the statement will be executed. That is why we use exception handling in Java. Do You Know? What is the difference between checked and unchecked exceptions? What happens behind the code int data=50/0;? Why use multiple catch block? Is there any possibility when finally block is not executed? What is exception propagation? What is the difference between throw and throws keyword? What are the 4 rules for using exception handling with method overriding? Hierarchy of Java Exception classes The java.lang.Throwable class is the root class of Java Exception hierarchy which is inherited by two subclasses: Exception and Error. A hierarchy of Java Exception classes are given below: Types of Java Exceptions There are mainly two types of exceptions: checked and unchecked. Here, an error is considered as the unchecked exception. According to Oracle, there are three types of exceptions: Checked Exception Unchecked Exception Error 1) Checked Exception The classes which directly inherit Throwable class except RuntimeException and Error are known as checked exceptions e.g. IOException, SQLException etc. Checked exceptions are checked at compile-time. 2) Unchecked Exception The classes which inherit RuntimeException are known as unchecked exceptions e.g. ArithmeticException, NullPointerException, ArrayIndexOutOfBoundsException etc. Unchecked exceptions are not checked at compile-time, but they are checked at runtime. 3) Error Error is irrecoverable e.g. OutOfMemoryError, VirtualMachineError, AssertionError etc. Keyword Description try The "try" keyword is used to specify a block where we should place exception code. The try block must be followed by either catch or finally. It means, we can't use try block alone. catch The "catch" block is used to handle the exception. It must be preceded by try block which means we can't use catch block alone. It can be followed by finally block later. finally The "finally" block is used to execute the important code of the program. It is executed whether an exception is handled or not. throw The "throw" keyword is used to throw an exception. throws The "throws" keyword is used to declare exceptions. It doesn't throw an exception. It specifies that there may occur an exception in the method. It is always used with method signature.

finally block:

package com.cerotid.exceptionhandling;

public class FinallyBlockDemo {

       public static void main(String[] args) {

try

{

       System.out.println("try");

}

catch(ArithmeticException ae)

{

       System.out.println("catch");

}

finally

{

       System.out.println("finally");

}

       }

}