Design patterns represent the best practices used by experienced
object-oriented software developers. Design patterns are solutions to
general problems that software developers faced during software
development.
These solutions were obtained by trial and error by numerous software
developers over quite a substantial period of time.
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Sunday, January 15, 2017
Design Pattern - Factory Pattern
Factory pattern is one of the most used design patterns in Java. This
type of design pattern comes under creational pattern as this pattern
provides one of the best ways to create an object.
Design Pattern - Abstract Factory Pattern
Abstract Factory patterns work around a super-factory which creates
other factories. This factory is also called as factory of factories.
This type of design pattern comes under creational pattern as this
pattern provides one of the best ways to create an object.
Design Pattern - Singleton Pattern
Singleton pattern is one of the simplest design patterns in Java.
This type of design pattern comes under creational pattern as this
pattern provides one of the best ways to create an object.
Design Patterns - Builder Pattern
Builder pattern builds a complex object using simple objects and
using a step by step approach. This type of design pattern comes under
creational pattern as this pattern provides one of the best ways to
create an object.
Design Patterns - Prototype Pattern
Prototype pattern refers to creating duplicate object while keeping
performance in mind. This type of design pattern comes under creational
pattern as this pattern provides one of the best ways to create an
object.
Design Patterns - Adapter Pattern
Adapter pattern works as a bridge between two incompatible
interfaces. This type of design pattern comes under structural pattern
as this pattern combines the capability of two independent interfaces.
Design Patterns - Bridge Pattern
Bridge is used when we need to decouple an abstraction from its
implementation so that the two can vary independently. This type of
design pattern comes under structural pattern as this pattern decouples
implementation class and abstract class by providing a bridge structure
between them.
Design Patterns - Filter Pattern
Filter pattern or Criteria pattern is a design pattern that enables
developers to filter a set of objects using different criteria and
chaining them in a decoupled way through logical operations. This type
of design pattern comes under structural pattern as this pattern
combines multiple criteria to obtain single criteria.
Design Patterns - Composite Pattern
Composite pattern is used where we need to treat a group of objects
in similar way as a single object. Composite pattern composes objects in
term of a tree structure to represent part as well as whole hierarchy.
This type of design pattern comes under structural pattern as this
pattern creates a tree structure of group of objects.
Design Patterns - Decorator Pattern
Decorator pattern allows a user to add new functionality to an
existing object without altering its structure. This type of design
pattern comes under structural pattern as this pattern acts as a wrapper
to existing class.
This pattern creates a decorator class which wraps the original class and provides additional functionality keeping class methods signature intact.
This pattern creates a decorator class which wraps the original class and provides additional functionality keeping class methods signature intact.
Design Patterns - Facade Pattern
Facade pattern hides the complexities of the system and provides an
interface to the client using which the client can access the system.
This type of design pattern comes under structural pattern as this
pattern adds an interface to existing system to hide its complexities.
Design Patterns - Flyweight Pattern
Flyweight pattern is primarily used to reduce the number of objects
created and to decrease memory footprint and increase performance. This
type of design pattern comes under structural pattern as this pattern
provides ways to decrease object count thus improving the object
structure of application.
Design Patterns - Proxy Pattern
In proxy pattern, a class represents functionality of another class. This type of design pattern comes under structural pattern.
In proxy pattern, we create object having original object to interface its functionality to outer world.
In proxy pattern, we create object having original object to interface its functionality to outer world.
Chain of Responsibility Pattern
As the name suggests, the chain of responsibility pattern creates a
chain of receiver objects for a request. This pattern decouples sender
and receiver of a request based on type of request. This pattern comes
under behavioral patterns.
Design Patterns - Command Pattern
Command pattern is a data driven design pattern and falls under
behavioral pattern category. A request is wrapped under an object as
command and passed to invoker object. Invoker object looks for the
appropriate object which can handle this command and passes the command
to the corresponding object which executes the command.
Design Patterns - Interpreter Pattern
Interpreter pattern provides a way to evaluate language grammar or
expression. This type of pattern comes under behavioral pattern. This
pattern involves implementing an expression interface which tells to
interpret a particular context. This pattern is used in SQL parsing,
symbol processing engine etc.
Design Patterns - Iterator Pattern
Iterator pattern is very commonly used design pattern in Java and
.Net programming environment. This pattern is used to get a way to
access the elements of a collection object in sequential manner without
any need to know its underlying representation.
Iterator pattern falls under behavioral pattern category.
Iterator pattern falls under behavioral pattern category.
Design Patterns - Mediator Pattern
Mediator pattern is used to reduce communication complexity between
multiple objects or classes. This pattern provides a mediator class
which normally handles all the communications between different classes
and supports easy maintenance of the code by loose coupling. Mediator
pattern falls under behavioral pattern category.
Design Patterns - Memento Pattern
Memento pattern is used to restore state of an object to a previous
state. Memento pattern falls under behavioral pattern category.
Design Patterns - Observer Pattern
Observer pattern is used when there is one-to-many relationship
between objects such as if one object is modified, its depenedent
objects are to be notified automatically. Observer pattern falls under
behavioral pattern category.
Design Patterns - State Pattern
In State pattern a class behavior changes based on its state. This type of design pattern comes under behavior pattern.
In State pattern, we create objects which represent various states and a context object whose behavior varies as its state object changes.
In State pattern, we create objects which represent various states and a context object whose behavior varies as its state object changes.
Design Patterns - Null Object Pattern
In Null Object pattern, a null object replaces check of NULL object
instance. Instead of putting if check for a null value, Null Object
reflects a do nothing relationship. Such Null object can also be used to
provide default behaviour in case data is not available.
Design Patterns - Strategy Pattern
In Strategy pattern, a class behavior or its algorithm can be changed
at run time. This type of design pattern comes under behavior pattern.
Design Patterns - Template Pattern
In Template pattern, an abstract class exposes defined
way(s)/template(s) to execute its methods. Its subclasses can override
the method implementation as per need but the invocation is to be in the
same way as defined by an abstract class. This pattern comes under
behavior pattern category.
Design Patterns - Visitor Pattern
In Visitor pattern, we use a visitor class which changes the
executing algorithm of an element class. By this way, execution
algorithm of element can vary as and when visitor varies. This pattern
comes under behavior pattern category. As per the pattern, element
object has to accept the visitor object so that visitor object handles
the operation on the element object.
Design Patterns - MVC Pattern
MVC Pattern stands for Model-View-Controller Pattern. This pattern is used to separate application's concerns.
Design Patterns - Business Delegate Pattern
Business Delegate Pattern is used to decouple presentation tier and
business tier. It is basically use to reduce communication or remote
lookup functionality to business tier code in presentation tier code. In
business tier we have following entities.
Design Patterns - Composite Entity Pattern
Composite Entity pattern is used in EJB persistence mechanism. A
Composite entity is an EJB entity bean which represents a graph of
objects. When a composite entity is updated, internally dependent
objects beans get updated automatically as being managed by EJB entity
bean. Following are the participants in Composite Entity Bean.
Data Access Object Pattern
Data Access Object Pattern or DAO pattern is used to separate low
level data accessing API or operations from high level business
services. Following are the participants in Data Access Object Pattern.
Design Pattern - Front Controller Pattern
The front controller design pattern is used to provide a centralized
request handling mechanism so that all requests will be handled by a
single handler. This handler can do the authentication/ authorization/
logging or tracking of request and then pass the requests to
corresponding handlers. Following are the entities of this type of
design pattern.
Design Pattern - Intercepting Filter Pattern
The intercepting filter design pattern is used when we want to do
some pre-processing / post-processing with request or response of the
application. Filters are defined and applied on the request before
passing the request to actual target application.
Design Pattern - Service Locator Pattern
The service locator design pattern is used when we want to locate
various services using JNDI lookup. Considering high cost of looking up
JNDI for a service, Service Locator pattern makes use of caching
technique. For the first time a service is required, Service Locator
looks up in JNDI and caches the service object.
Design Pattern - Transfer Object Pattern
The Transfer Object pattern is used when we want to pass data with
multiple attributes in one shot from client to server. Transfer object
is also known as Value Object. Transfer Object is a simple POJO class
having getter/setter methods and is serializable so that it can be
transferred over the network.
Design Patterns Questions and Answers
Design Patterns Questions and Answers has been designed with a special intention of helping students and professionals preparing for various Certification Exams and Job Interviews.
This section provides a useful collection of sample Interview Questions
and Multiple Choice Questions (MCQs) and their answers with
appropriate explanations.
Design Pattern - Useful Resources
The following resources contain additional information on Design
Patterns. Please use them to get more in-depth knowledge on this.
Discuss Design Pattern
Design patterns represent the best practices used by experienced
object-oriented software developers. Design patterns are solutions to
general problems that software developers faced during software
development. These solutions were obtained by trial and error by
numerous software developers over quite a substantial period of time.
This tutorial will take you through step by step approach and examples
using Java while learning Design Pattern concepts.
AWT - Overview
Graphical User Interface
Graphical User Interface (GUI) offers user interaction via some graphical components. For example our underlying Operating System also offers GUI via window,frame,Panel, Button, Textfield, TextArea, Listbox, Combobox, Label, Checkbox etc. These all are known as components. Using these components we can create an interactive user interface for an application.AWT Environment Setup
This section guides you on how to download and set up Java on your
machine. Please follow the following steps to set up the environment.
AWT Controls
Every user interface considers the following three main aspects:
- UI elements : Thes are the core visual elements the user
eventually sees and interacts with. GWT provides a huge list of widely
used and common elements varying from basic to complex which we will
cover in this tutorial.
AWT Event Handling
What is an Event?
Change in the state of an object is known as event i.e. event describes the change in state of source. Events are generated as result of user interaction with the graphical user interface components.AWT Event Classes
The Event classes represent the event. Java provides us various Event
classes but we will discuss those which are more frequently used.
AWT Event Listeners
The Event listener represent the interfaces responsible to handle
events. Java provides us various Event listener classes but we will
discuss those which are more frequently used. Every method of an event
listener method has a single argument as an object which is subclass of
EventObject class.
AWT Event Adapters
Adapters are abstract classes for receiving various events. The
methods in these classes are empty. These classes exists as convenience
for creating listener objects.
AWT Layouts
Introduction
Layout means the arrangement of components within the container. In other way we can say that placing the components at a particular position within the container. The task of layouting the controls is done automatically by the Layout Manager.AWT Containers
Containers are integral part of AWT GUI components. A container
provides a space where a component can be located. A Container in AWT is
a component itself and it adds the capability to add component to
itself. Following are noticable points to be considered.
AWT Menu Classes
As we know that every top-level window has a menu bar associated with
it. This menu bar consist of various menu choices available to the end
user. Further each choice contains list of options which is called drop
down menus. Menu and MenuItem controls are subclass of MenuComponent
class.
AWT Graphics Classes
Graphics controls allows application to draw onto the component or on image.
Graphics Controls
AWT - Useful Resources
The following resources contain additional information on AWT. Please use them to get more in-depth knowledge on this topic.
Discuss AWT
JAVA provides a rich set of libraries to create Graphical User Interface
in platform independent way. In this article we'll look in AWT
(Abstract Window Toolkit).
Apache POI Overview
Many a time, a software application is required to generate reports
in Microsoft Excel file format. Sometimes, an application is even
expected to receive Excel files as input data. For example, an
application developed for the Finance department of a company will be
required to generate all their outputs in Excel.
Apache POI - Java Excel APIs
This chapter takes you through some of the flavors of Java Excel API
and their features. There are many vendors who provide Java Excel
related APIs; some of them are considered in this chapter.
Apache POI Environment
This chapter takes you through the process of setting up Apache POI
on Windows and Linux based systems. Apache POI can be easily installed
and integrated with your current Java environment following a few simple
steps without any complex setup procedures. User administration is
required while installation.
POI – Core Classes
This chapter explains a few classes and methods under the Apache POI
API that are critical to work on Excel files using Java programs.
Apache POI – Workbooks
Here the term 'Workbook' means Microsoft Excel file. After completion
of this chapter, you will be able to create new Workbooks and open
existing Workbooks with your Java program.
Apache POI – Spreadsheets
This chapter explains how to create a spreadsheet and manipulate it
using Java. Spreadsheet is a page in an Excel file; it contains rows and
columns with specific names.
Apache POI – Cells
Any data that you enter into a spreadsheet is always stored in a
cell. We use the labels of rows and columns to identify a cell. This
chapter describes how to manipulate data in cells in a spreadsheet using
Java programming.
Apache POI – Fonts
This chapter explains how to set different fonts, apply styles, and
display text in different angles of direction in an Excel spreadsheet.
Apache POI – Formula
This chapter takes you through the process of applying different
formulas on cells using Java programming. The basic purpose of Excel
application is to maintain numerical data by applying formulas on it.
Apache POI – Hyperlink
This chapter explains how to add hyperlinks to the contents in a
cell. Usually hyperlinks are used to access any web URL, email, or an
external file.
Apache POI – Print Area
This chapter explains how to set the print area on a spreadsheet. The
usual print area is from left top to right bottom on Excel
spreadsheets. Print area can be customized according to your
requirement. It means you can print a particular range of cells from the
whole spreadsheet, customize the paper size, print the contents with
the grid lines turned on, etc.
Apache POI - Database
This chapter explains how the POI library interacts with a database.
With the help of JDBC, you can retrieve data from a database and insert
that data into a spreadsheet using the POI library. Let us consider
MySQL database for SQL operations.
Apache POI Quick Guide
Apache POI Overview
Many a time, a software application is required to generate reports in Microsoft Excel file format. Sometimes, an application is even expected to receive Excel files as input data. For example, an application developed for the Finance department of a company will be required to generate all their outputs in Excel.Apache POI - Useful Resources
The following resources contain additional information on Apache POI.
Please use them to get more in-depth knowledge on this topic.
Discuss Apache POI
This tutorial provides a basic understanding of Apache POI library
and its features. Apache POI is a popular API that allows programmers to
create, modify, and display MS Office files using Java programs. It is
an open source library developed and distributed by Apache Software
Foundation to design or modify Microsoft Office files using Java
program. It contains classes and methods to decode the user input data
or a file into MS Office documents.
Apache POI Word - Overview
Many a time, a software application is required to generate reference documents in Microsoft Word file format. Sometimes, an application is even expected to receive Word files as input data.
Apache POI Word - Installation
This chapter takes you through the process of setting up Apache POI on Windows and Linux based systems. Apache POI can be easily installed and integrated with your current Java environment, following a few simple steps without any complex setup procedures.
Apache POI Word - Core Classes
This chapter takes you through the classes and methods of Apache POI for managing a Word document.
Apache POI Word - Document
Here the term 'document' refers to a MS-Word file. After completion of this chapter, you will be able to create new documents and open existing documents using your Java program.
Apache POI Word - Paragraph
In this chapter you will learn how to create a Paragraph and how to add it to a document using Java. Paragraph is a part of a page in a Word file.
After completing this chapter, you will be able to create a Paragraph and perform read operations on it.
After completing this chapter, you will be able to create a Paragraph and perform read operations on it.
Apache POI Word - Borders
In this chapter, you will learn how to apply border to a paragraph using Java programming.
Apache POI Word - Tables
In this chapter, you will learn how to create a table of data in a document. You can create a table data by using XWPFTable class. By adding each Row to table and adding each cell to Row, you will get table data.
Apache POI Word - Font & Alignment
This chapter shows how to apply different font styles and alignments
in a Word document using Java. Generally, Font Style contains: Font
size, Type, Bold, Italic, and Underline. And Alignment is categorized
into left, center, right, and justify.
Apache POI Word - Text Extraction
This chapter explains how to extract simple text data from a Word
document using Java. In case you want to extract metadata from a Word
document, make use of Apache Tika.
Apache POI Word - Quick Guide
Apache POI Word - Overview
Many a time, a software application is required to generate reference documents in Microsoft Word file format. Sometimes, an application is even expected to receive Word files as input data.Apache POI Word - Useful Resources
The following resources contain additional information on Apache-POI
Word. Please use them to get more in-depth knowledge on this topic.
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