Bridge Pattern
Builder pattern provides
independence to the interface from its implementation. It provides flexibility
to both to vary independently. Suppose we have a database containing multiple
questions and we want to display the questions on the basis of the user
selections. Then such type of problems can be solved with the Bridge Design
Pattern. It does that simply by decoupling the relationship among the objects.
Benefits: It separates the abstraction
from the
implementation details. Inheritance tightly couples the abstraction with the
implementations at the compile time, However the Bridge pattern hides the implementation details, improves the extensibility, shares
an implementation among multiple objects. It reduces the number of subclasses,
sometimes use of pure inheritance increases the number of subclasses. It also
improves the extensibility by extending independency between the abstraction and
the implementation.
Usage: It is used in such situation if
you do not want the permanent binding between an abstraction and its
implementation. It is frequently used in those places where changes made
in the implementation does not effects the clients. It can be used to fulfill
such requirements where the abstractions and the implementations needs to be extensible.
Now lets take an example:
First develop a Question.java interface :
Question.java :
interface Question {
public void nextQuestion();
public void priorQuestion();
public void newQuestion(String q);
public void deleteQuestion(String q);
public void displayQuestion();
public void displayAllQuestions();
}
|
Develop another class QuestionManager implementing
the Question.java interface :
class QuestionManager {
protected Question questDB;
public String catalog;
public QuestionManager(String catalog) {
this.catalog = catalog;
}
public void next() {
questDB.nextQuestion();
}
public void prior() {
questDB.priorQuestion();
}
public void newOne(String quest) {
questDB.newQuestion(quest);
}
public void delete(String quest) {
questDB.deleteQuestion(quest);
}
public void display() {
questDB.displayQuestion();
}
public void displayAll() {
System.out.println("Question Catalog: " + catalog);
questDB.displayAllQuestions();
}
}
|
Develop another class QuestionFormat extending
the QuestionManager class
QuestionFormat.java
class QuestionFormat extends QuestionManager {
public QuestionFormat(String catalog){
super(catalog);
}
public void displayAll() {
System.out.println("\n~~~~~~~~~~~~~~~~~~~~~~~~");
super.displayAll();
System.out.println("~~~~~~~~~~~~~~~~~~~~~~~~");
}
}
|
Develop another class JavaQuestions
implementing the
"Question" interface :
JavaQuestions.java:
import java.util.*;
class JavaQuestions implements Question {
private List <String> questions = new ArrayList<String>();
private int current = 0;
public JavaQuestions() {
questions.add("What is Java? ");
questions.add("What is marker interface? ");
questions.add("What is cross-platform? ");
questions.add("How multiple polymorphism
is achieved in java? ");
questions.add("How many types of exception
handling are there in java? ");
questions.add("Define the keyword final for
variable, method, and class
in java? ");
questions.add("What is multi-tasking? ");
questions.add("What is multi-threading? ");
}
public void nextQuestion() {
if( current <= questions.size() - 1 )
current++;
}
public void priorQuestion() {
if( current > 0 )
current--;
}
public void newQuestion(String quest) {
questions.add(quest);
}
public void deleteQuestion(String quest) {
questions.remove(quest);
}
public void displayQuestion() {
System.out.println( questions.get(current) );
}
public void displayAllQuestions() {
for (String quest : questions) {
System.out.println(quest);
}
}
}
|
Develop another class TestBridge.
TestBridge.java
class TestBridge {
public static void main(String[] args) {
QuestionFormat questions = new QuestionFormat
"Java Language");
questions.questDB = new JavaQuestions();
// questions.questDB = new CsharpQuestions();
// questions.questDB = new CplusplusQuestions();
questions.display();
questions.next();
questions.newOne("What is polymorphism? ");
questions.newOne("How many types of polymorphism
are there in java?");
questions.displayAll();
}
}
|
Here is the output of the above program:
C:\ Command Prompt
C:\> javac TestBridge.java
C:\> java TestBridge
What is Java?
~~~~~~~~~~~~~~~~~~~~~~~~
Question Catalog: Java Language
What is Java?
What is marker interface?
What is cross-platform?
How multiple polymorphism is achieved in java?
How many types of exception handling are there in java?
Define the keyword final for variable, method, and class in java?
What is multi-tasking?
What is multi-threading?
What is polymorphism?
How many types of polymorphism are there in java?
~~~~~~~~~~~~~~~~~~~~~~~~ |
The above example tries to show how the Bridge pattern
pattern decouples the interface from its implementation. One can easily
notice
that the class JavaQuestion can be launched independently working as an independent system.
|
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