The document discusses exception handling in Java. It defines exceptions, describes the exception hierarchy, and lists common checked and unchecked exceptions. It also explains how to implement exception handling using try, catch, throw, throws and finally. Methods for creating user-defined exceptions and using assertions are also covered. The document aims to teach readers how to identify, handle and throw exceptions to make Java programs more robust.

1. Exception Handling
Pre-assessment Questions
1. Which type of inheritance supports repeating inheritance?
a. Single level inheritance
b. Multiple inheritance
c. Multilevel inheritance
d. Multipath inheritance
2. Which keyword is used to define the constants in an interface?
a. super
b. public
c. private
d. final
©NIIT Programming in Java Lesson 1B / Slide 1 of 25

2. Exception Handling
Pre-assessment Questions (Contd.)
3. Which concept of object-oriented programming is used in method overriding?
a. Polymorphism
b. Abstraction
c. Encapsulation
d. Inheritance
4. What is the return type of the methods declared in an interface?
a. Default
b. private
c. protected
d. public
©NIIT Programming in Java Lesson 1B / Slide 2 of 25

3. Exception Handling
Pre-assessment Questions (Contd.)
5. Which type of inheritance enables you to inherit class data members and
methods from more than one superclass?
• Single level inheritance
• Multiple inheritance
• Multilevel inheritance
• Multipath inheritance
©NIIT Programming in Java Lesson 1B / Slide 3 of 25

4. Exception Handling
Solutions to Pre-assessment
Questions
1. b. Multiple inheritance
2. d. final
3. a. Polymorphism
4. d. public
5. b. Multiple inheritance
©NIIT Programming in Java Lesson 1B / Slide 4 of 25

5. Exception Handling
Objectives
• In this lesson, you will learn to:
• Identify the various types of exceptions in Java
• Handle exceptions by using the try, catch, and finally clauses
• Use the throw statement
• Implement user-defined exceptions
• Use assertions in Java
©NIIT Programming in Java Lesson 1B / Slide 5 of 25

6. Exception Handling
Exceptions in Java
• An exception can be defined as an abnormal event that occurs during program
execution and disrupts the normal flow of instructions.
• Errors in a Java program are categorized into two groups:
• Compile-time errors
• Run Time errors
• Concept of Exceptions:
• The unexpected situations that occur during program execution are:
• Running out of memory
• Resource allocation errors
• Inability to find files
• Problems in network connectivity
©NIIT Programming in Java Lesson 1B / Slide 6 of 25

7. Exception Handling
Exceptions in Java (Contd.)
• Exception Classes
• The following figure shows the Exception class heirarchy:
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8. Exception Handling
Exceptions in Java (Contd.)
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9. Exception Handling
Exceptions in Java (Contd.)
• Built-in Exceptions
• Java consists of the following categories of built-in exceptions:
• Checked Exceptions
• Unchecked Exceptions
©NIIT Programming in Java Lesson 1B / Slide 9 of 25

10. Exception Handling
Exceptions in Java (Contd.)
• The following table lists the various checked exceptions in Java:
Exception Cause of Creation
ClassNotFoundException Occurs when the Java run time system
is unable to find the class referred.
IllegalAccessException Occurs when you want to refer a class
that is not accessible.
InstantiationException Occurs when you try to create an
object of an abstract class or interface.
NoSuchMethodException Occurs when you call a method that
does not exist.
©NIIT Programming in Java Lesson 1B / Slide 10 of 25

11. Exception Handling
Exceptions in Java (Contd.)
• The following table lists the various unchecked exceptions:
Exception Cause of Creation
ArithmeticException Occurs when you make an
arithmetic error, such as dividing a
number by zero.
ArrayIndexOutOfBoundsException Occurs when an attempt is made to
access an array element beyond
the index of the array.
ArrayStoreException Occurs when you assign an
element to an array that is not
compatible with the data type of
that array.
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12. Exception Handling
Exceptions in Java (Contd.)
Exception Cause of Creation
ClassCastException Occurs when you assign a
reference variable of a class to an
incompatible reference variable of
another class.
IllegalArgumentException Occurs when you pass an
argument of incompatible data
type to a method.
NegativeArraySizeException Occurs when you create an array
with negative size.
©NIIT Programming in Java Lesson 1B / Slide 12 of 25

13. Exception Handling
Exceptions in Java (Contd.)
Exception Cause of Creation
NullPointerException Occurs when an application tries to
use an object without allocating
memory to it or calls a method of a
null object.
NumberFormatException Occurs when you want to convert a
string in an incorrect format to a
numeric format.
©NIIT Programming in Java Lesson 1B / Slide 13 of 25

14. Exception Handling
Implementing Exception Handling
• You can implement exception-handling in a program by using the following
keywords:
• try
• catch
• throw
• throws
• finally
• Using try and catch statements
• The try block encloses the statements that might raise an exception
within it and defines the scope of the exception handlers associated
with it.
• The catch block is used as an exception-handler. You enclose the
code that you want to monitor inside a try block to handle a run time
error.
©NIIT Programming in Java Lesson 1B / Slide 14 of 25

15. Exception Handling
Implementing Exception Handling
(Contd.)
• The following syntax shows how to declare the try-catch block:
try
{
// Statements that cause an exception.
}
catch(ExceptionName obj)
{
// Error handling code.
}
• Using multiple catch statements
• A single try block can have many catch blocks. This is necessary when
the try block has statements that raise different types of exceptions.
©NIIT Programming in Java Lesson 1B / Slide 15 of 25

16. Exception Handling
Implementing Exception Handling
(Contd.)
• The multiple catch blocks generate unreachable code error.
• If the first catch block contains the Exception class object then the
subsequent catch blocks are never executed.
• The Exception class being the superclass of all the exception classes catches
various types of exceptions. The Java compiler gives an error stating that the
subsequent catch blocks have not been reached.
• This is known as the unreachable code problem.
• To avoid unreachable code error, the last catch block in multiple catch
blocks must contain the Exception class object.
• Using the finally clause
• The finally block is used to process certain statements, no matter whether
an exception is raised or not.
©NIIT Programming in Java Lesson 1B / Slide 16 of 25

17. Exception Handling
Implementing Exception Handling
(Contd.)
• The following syntax shows how to declare the try-finally
block:
try
{
// Block of code
}
finally
{
// Block of code that is always executed irrespective of
an exception being raised or not.
}
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18. Exception Handling
Throwing an Exception
• Using the throw statement
• The throw statement causes termination of the normal flow of control of the
Java code and stops the execution of the subsequent statements if an
exception is thrown when the throw statement is executed.
• The throw clause transfers the control to the nearest catch block handling the
type of exception object throws.
• The following syntax shows how to declare the throw statement:
throw ThrowableObj
• Using the throws statement
• The throws statement is used by a method to specify the types of exceptions
the method throws.
• If a method is capable of raising an exception that it does not handle, the
method must specify that the exception has to be handled by the calling
method.
• This is done using the throws statement.
©NIIT Programming in Java Lesson 1B / Slide 18 of 25

19. Exception Handling
Implementing User-Defined Exception
• The user-defined Exception class also inherits the methods defined in the
Throwable class.
• The following table lists the various methods defined by the Throwable
class:
Methods Description
String getMessage() Returns a description of the
exception
String toString() Returns a string object containing a
description of the exception.
Throwable fillInStackTrace() Returns a Throwable object that
contains a stack trace
void printStackTrace() Prints the stack trace
©NIIT Programming in Java Lesson 1B / Slide 19 of 25

20. Exception Handling
Demonstration-Exception Handling in
Java
• Problem Statement
• System Software Solutions Inc. needs to store the details, such as
name, age, and ID of three employees of the company. While
storing the details of the employees, the record of an employee
was entered twice and hence the record of the third employee
could not be displayed. Identify the exception that is raised if the
details of all the employees were stored. Use the try- catch block
to handle the exception.
©NIIT Programming in Java Lesson 1B / Slide 20 of 25

21. Exception Handling
Demonstration-Exception Handling in
Java (Contd.)
• Solution
• To solve the above problem, perform the following tasks:
• Identify the type of error and the code segment in which
the error occurs.
• Identify the mechanism of trapping the exception.
• Code the application
• Compile and execute the application
©NIIT Programming in Java Lesson 1B / Slide 21 of 25

22. Exception Handling
Assertions in Java
• Assertions are the checks provided by the Java language to ensure that any
assumption made at the start of a program is true throughout the program.
• Assertions:
• Assertions are statements in Java that enable you to test the
assumptions made in a program during program execution.
• An assertion statement contains a boolean expression that the
programmer believes to be true at the time the statement is executed.
• Assertions are used during testing of a program to ensure that the
specified condition is true.
• The following syntax shows how to declare an assertion using assert
statement in Java:
assert expressionA;
• The following syntax shows the compilation of the Java program named
AssertDemo.java that is using assert statement:
javac -source 1.4 AssertDemo.java
©NIIT Programming in Java Lesson 1B / Slide 22 of 25

23. Exception Handling
Assertions in Java (Contd.)
• The syntax to enable assertion in a specified class with –ea option is: .
java –ea: AssertDemo
• The syntax to disable assertion in a specified class with –da option is:
java –da: AssertDemo
©NIIT Programming in Java Lesson 1B / Slide 23 of 25

24. Exception Handling
Summary
In this lesson, you learned:
• Errors can be broadly categorized into two groups on the basis of
whether the compiler is able to handle the error or not, such as compile
time errors and run time errors.
• An exception is a run time error that can be defined as an abnormal
event that occurs during the execution of a program and disrupts the
normal flow of instructions.
• In Java, the Throwable class is the superclass of all the exception
classes. It is the class at the top position in the exception class
hierarchy. The Exception class and the Error class are two direct
subclasses of the Throwable class.
• The built-in exceptions in Java are divided into two types on the basis of
the conditions where the exception is raised:
• Checked Exceptions or Compiler-enforced Exceptions
• Unchecked exceptions or Runtime Exceptions
©NIIT Programming in Java Lesson 1B / Slide 24 of 25

25. Exception Handling
Summary (Contd.)
• You can implement exception handling in your program by using the
following keywords:
• try
• catch
• throw
• throws
• finally
• You use multiple catch blocks to throw more than one type of exception.
• The finally clause is used to execute the statements that need to be
executed whether or not an exception has been thrown.
• The throw statement causes termination of the normal flow of control of
the Java code and stops the execution of subsequent statements after
the throw statement.
• The throws clause is used by a method to specify the types of
exceptions the method throws.
• You can create your own exception classes to handle the situations
specific to an application
©NIIT Programming in Java Lesson 1B / Slide 25 of 25