tài liệu tự học java cho người mới bắt đầu

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... Access Class variables Can also be

Session 6

Module 8: More on Classes Module 9: Exceptions

Module 7 - Review

 Inheritance

 Overloading of methods

 Using abstract keyword

 Using final keywords

 Interfaces

Module 8 - Objectives

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

Access Class variables

 Can also be manipulated without creating an instance of the class

 Are referenced by the class name itself

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.

Accessing class method

 The static initialization block

can reference only class

variables that have been

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

Different type of nested class

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

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

Anonymous classes

 An anonymous class does not have a name It is a type of local class.

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.

Module 9 - Objectives

 Introduction to Exceptions

 Exception handling in Java

 User defined exceptions

 Assertions

Introduction to Exceptions

Explain the concept of Exceptions

 An exception are errors that

arises at runtime.

 Exceptions object describles

detail of error.

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

Classification of Exceptions

 Checked Exceptions

 Unchecked

Exceptions

Types of Checked Exceptions

All Checked exceptions are derived from the Exception class.

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

Types of Unchecked Exceptions

All Unchecked exceptions are directly or indirectly derived from the RuntimeException class

Exception handling in Java

The use of try-catch block

The use of multiple catch block

The use of finally block:

The use of throw and throws keyword

The use of throw and throws keyword

exception in a method.

raise any checked or unchecked exception that

it does not handle and enables the caller of the method to guard themselves against exception Except for Error or RuntimeException and their

User defined exception

User defined exception classes are subclassed from the base class Exception These exceptions are handled and thrown in the same manner as predefined exceptions.

Assertions

Using the assert statement

First form

Using the assert statement

Second form

Enabling and Disabling Assertions

Where to use Assertions

Why to use Assertions

Module 8,9 - Summary