Exceptions in Java -II

Throwable Class 

The Throwable class provides a String variable that can be set by the subclasses to provide a detail message that provides more information of the exception occurred. All classes of throwables define a one-parameter constructor that takes a string as the detail message.

The class Throwable provides getMessage() function to retrieve an exception. It has a printStackTrace() method to print the stack trace to the standard error stream. Lastly It also has a toString() method to print a short description of the exception. For more information on what is printed when the following messages are invoked, please refer the java docs.

Syntax

String getMessage()

void printStackTrace()

String toString()

Class Exception

The class Exception represents exceptions that a program faces due to abnormal or special conditions during execution. Exceptions can be of 2 types: Checked (Compile time Exceptions)/ Unchecked (Run time Exceptions).

Class RuntimeException

Runtime exceptions represent programming errors that manifest at runtime. For example

ArrayIndexOutOfBounds, NullPointerException and so on are all subclasses of the java.lang.RuntimeException class, which is a subclass of the Exception class. These are basically business logic programming errors.

Class Error

Errors are irrecoverable condtions that can never be caught. Example: Memory leak, LinkageError etc. Errors are direct subclass of Throwable class.

A Program Showing How the JVM throws an Exception at runtime

public class DivideException {

    public static void main(String[] args) {
        division(100,4);        // Line 1
        division(100,0);        // Line 2
        System.out.println("Exit main().");
    }

    public static void division(int totalSum, int totalNumber) {

        System.out.println("Computing Division.");
        int average  = totalSum/totalNumber;
        System.out.println("Average : "+ average);
    }
}
++++++++++++++++++++++++
An ArithmeticException is thrown at runtime when Line 11 is executed because integer division by 0 is an illegal operation. The “Exit main()” message is never reached in the main method
Output
Computing Division.
java.lang.ArithmeticException: / by zero
Average : 25
Computing Division.
at DivideException.division(DivideException.java:11)
at DivideException.main(DivideException.java:5)
Exception in thread “main”

Exceptions in java

Exceptions in java are any abnormal, unexpected events or extraordinary conditions that may occur at runtime. They could be file not found exception, unable to get connection exception and so on. On such conditions java throws an exception object. Java Exceptions are basically Java objects. No Project can never escape a java error exception.

Java exception handling is used to handle error conditions in a program systematically by taking the necessary action. Exception handlers can be written to catch a specific exception such as Number Format exception, or an entire group of exceptions by using a generic exception handlers. Any exceptions not specifically handled within a Java program are caught by the Java run time environment

An exception is a subclass of the Exception/Error class, both of which are subclasses of the Throwable class. Java exceptions are raised with the throw keyword and handled within a catch block.