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Session 6
Module 8: More on Classes
Module 9: Exceptions
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Module 7 - Review

Inheritance

Overloading of methods

Using abstract keyword

Using final keywords

Interfaces
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Module 8 - Objectives

Class variables

Nested class
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Class variables

Are declared using the static keyword

Once the value is modified, all instances of the class are
updated to share the same value
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Access Class variables


Can also be manipulated without creating an
instance of the class

Are referenced by the class name itself
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Static methods

Also known as class methods, do not have
reference to any instance variable in a class, used
to access class variables and methods.

The keyword this cannot be used inside a static
method.
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Accessing class method

Can be accessed by
using a class name

or

an instance name (not
recommend)
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Static initializer

Is a block of code embraced
in curly braces

It is preceded by the static

keyword

It initializes the static
variables in class

The static initialization block
can reference only class
variables that have been
declared before it
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Nested class

A class defined within another class

It can have access to members of the outer class
(enclosing class) even if the members are declared
private

It can be used for:

Allow logical grouping of classes

Increases encapsulation

More maintainable code
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Different type of nested class

Member classes or non-static nested classes


Local classes

Anonymous classes

Static nested classes
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Member classes or
non-static nested classes

It can access all fields and methods of the
outer class, but the reverse is not true.

An outer class cannot access a member of
an inner class even if it is declared as public
because members of an inner class are
declared within the scope of inner class
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Local classes
A local class is declared within a method,
constructor or an initializer.
In other words, a local class is declared within a
block of code and is visible only within that
particular block.
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Anonymous classes

An anonymous class does not have a name. It is a type of local
class.
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Static nested classes


A static nested class is
associated with its outer class.

It cannot refer directly to
instance variables or methods
defined in its enclosing class,
but it can access class
methods or variables directly.

An object needs to be
instantiated to access the
instance variables and
methods of the enclosing
class.
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Module 9 - Objectives

Introduction to Exceptions

Exception handling in Java

User defined exceptions

Assertions
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Introduction to Exceptions

Explain the concept of Exceptions


Identify the different types of Exceptions

Knowledge Check
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Explain the concept of Exceptions

An exception are errors that
arises at runtime.

Exceptions object describles
detail of error.
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Causes for Exceptions

Program errors

Arise due to errors present in APIs, such as NullPointerException

Program using these APIs cannot do anything about these errors

Client code errors

Arise when client code attempts operations, such as reading content
from a file without opening it.

Exception will provide information about the cause of the error

Can be handled by client code

Errors beyond the control of a program


Raised by runtime environment, such as memory error or network
connection failure error.

These exceptions that are not expected to be caught by the client
code
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Classification of Exceptions

Checked Exceptions

Unchecked
Exceptions
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Checked Exceptions

Generated in situations that occur during the normal
execution of a program. For example:

Requesting for missing file, invalid user input, and network
failures.

These exceptions should be handled to avoid
compile-time errors. It is checked during the
compilation.
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Types of Checked Exceptions
All Checked exceptions are derived from the Exception class.
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Unchecked Exceptions


Generated in situations that are considered non-recoverable for
a program (generated during the execution of the program). For
example:

Attempting to access an element beyond the maximum length of
an array.

An application is not required to check for these kinds of
exceptions.
Unchecked Exceptions
RuntimeException class Error class
(ex: logical bugs)
(ex: Out Of Memory Error)
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Types of Unchecked Exceptions
All Unchecked exceptions are directly or indirectly derived from the
RuntimeException class
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Exception handling in Java

State the use of try-catch block

Describe the use of finally block

State the flow of execution in an exception
handling block

Describe the use of throw and throws
keyword


Describe the use of multiple catch block
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The use of try-catch block
try {
Statement_1;
Statement_2;
…
}
catch(ExceptionType ObjectName){
Statement_1;
}
Syntax