What is meant by Bridge Design Pattern?

BRIDGE DESIGN PATTERN:Decouple an abstraction or interface from its implementation so that the two can vary independently.

  Where to use & benefits

• Want to separate abstraction and implementation permanently
• Share an implementation among multiple objects
• Want to improve extensibility
• Hide implementation details from clients
• Related patterns include 

EXAMLPE:

import java.util.*;

//abstraction
interface Question {
  
    public void nextQuestion();
    public void priorQuestion();
    public void newQuestion(String q);
    public void deleteQuestion(String q);
    public void displayQuestion();
    public void displayAllQuestions();
}

//implementation
class QuestionManager {
 
  protected Question questDB; //instantiate it later 
  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();
  }
}


//further implementation
class QuestionFormat extends QuestionManager {
  
    public QuestionFormat(String catalog){
        super(catalog);
    }

    public void displayAll() {
    
        System.out.println("\n~~~~~~~~~~~~~~~~~~~~~~~~");
        super.displayAll();
        System.out.println("~~~~~~~~~~~~~~~~~~~~~~~~");
    }
}

//decoupled implementation
class JavaQuestions implements Question {
  
    private List questions = new ArrayList();
    private int current = 0;

    public JavaQuestions() {
        //load from a database and fill in the container
        questions.add("What is Java? ");
        questions.add("What is an interface? ");
        questions.add("What is cross-platform? ");
        questions.add("What is UFT-8? ");
        questions.add("What is abstract? ");
        questions.add("What is Thread? ");
        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);
        }
    }
}


class TestBridge {
    public static void main(String[] args) {
 
        QuestionFormat questions = new QuestionFormat("Java Language");

        questions.questDB = new JavaQuestions();//can be hooked up with other question class
        //questions.questDB = new CsharpQuestions();
        //questions.questDB = new CplusplusQuestions();

        questions.display();
        questions.next();
    
        questions.newOne("What is object? ");
        questions.newOne("What is reference type?");

        questions.displayAll();
  }

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