Adapter Design Pattern – Implementation [Language Translator]

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Introduction

The Adapter Design Pattern is a structural design pattern that allows classes with incompatible interfaces to collaborate. A very natural real-world metaphor for this pattern is a Language Translator: imagine a person who speaks English wanting to communicate with someone who speaks French. Without an intermediary, direct communication is impossible. A translator acts as an adapter, listening to English, translating it to French, and vice versa.

Adapter Pattern Mapping

Pattern Role	Component in Example	Description
Client	EnglishSpeaker	Understands and speaks English words only
Target Interface	ITarget	Defines the interface expected by the client (e.g., translateAndTalk())
Adaptee	FrenchSpeaker	Existing class that understands only French
Adapter	TranslatorAdapter	Translates messages between English and French seamlessly

Java Code Implementation

1. Adaptee: FrenchSpeaker

public class FrenchSpeaker {
    public void speakFrench(String words) {
        System.out.println("French speaker receives: " + words);
    }

    public String replyInFrench() {
        return "Très bien, merci!";
    }
}

2. Target Interface: ITarget

public interface ITarget {
    void speakEnglish(String words);
    String receiveReplyInEnglish();
}

3. Adapter: TranslatorAdapter

public class TranslatorAdapter implements ITarget {
    private FrenchSpeaker frenchSpeaker = new FrenchSpeaker();

    @Override
    public void speakEnglish(String words) {
        System.out.println("Adapter translates English: \"" + words + "\" to French");
        String frenchTranslation = convertToFrench(words);
        frenchSpeaker.speakFrench(frenchTranslation);
    }

    @Override
    public String receiveReplyInEnglish() {
        String frenchReply = frenchSpeaker.replyInFrench();
        System.out.println("Adapter receives French reply: \"" + frenchReply + "\"");
        return convertToEnglish(frenchReply);
    }

    private String convertToFrench(String englishWords) {
        if ("Hello, how are you?".equalsIgnoreCase(englishWords)) {
            return "Bonjour, comment allez-vous?";
        }
        return "Bonjour!";
    }

    private String convertToEnglish(String frenchWords) {
        if ("Très bien, merci!".equalsIgnoreCase(frenchWords)) {
            return "Very well, thank you!";
        }
        return "Thank you!";
    }
}

4. Client: EnglishSpeaker

public class EnglishSpeaker {
    public static void main(String[] args) {
        ITarget translator = new TranslatorAdapter();

        System.out.println("English Speaker says: Hello, how are you?\n");
        translator.speakEnglish("Hello, how are you?");

        System.out.println();
        String reply = translator.receiveReplyInEnglish();
        System.out.println("English Speaker hears: " + reply);
    }
}

Console Output

English Speaker says: Hello, how are you?

Adapter translates English: "Hello, how are you?" to French
French speaker receives: Bonjour, comment allez-vous?

Adapter receives French reply: "Très bien, merci!"
English Speaker hears: Very well, thank you!

Related Tutorials from Ram N Java

• Adapter Design Pattern Implementation: Object Adapter Example
• Adapter Design Pattern Implementation: Class Adapter Example
• Adapter Design Pattern Implementation: Mobile Charger Example
• Adapter Design Pattern in Action: Real-World JDBC Driver Example

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Adapter Design Pattern – Implementation [Language Translator]

Adapter Design Pattern – Implementation [Language Translator] - Class Diagram

ITarget.java

public interface ITarget

{

public String translateAndTellToOtherPerson(String words,String convertToWhichLanguage);

}

John.java

import java.util.HashMap;

/*
 *  John can speak and understand English and French,he acts as a Adapter or Translator
 */
public class John implements ITarget
{

static HashMap<String, String> englishFrenchMap = new HashMap<String, String>();
static HashMap<String, String> frenchEnglishMap = new HashMap<String, String>();
David david = new David();
Rohit rohit =new Rohit();

static
{
englishFrenchMap.put("how are you?", "comment allez-vous?");
englishFrenchMap.put("I am in USA", "Je suis aux Etats-Unis");
frenchEnglishMap.put("Je suis très bien", "I am fine");
frenchEnglishMap.put("où êtes-vous?", "where are you?");

}

@Override
public String translateAndTellToOtherPerson( String words, String convertToWhichLanguage )
{
if( convertToWhichLanguage.equalsIgnoreCase("English") )
{

String englishWords = convertToEnglish(words);
System.out.println("\nJohn Converted \"" + words + " \" to \"" + englishWords
               + " and send the question to David");
String englishWordsReply = david.answerFortheQuestion(englishWords);
System.out.println("John Got reply from David in English like : " + "\"" + englishWordsReply
               + "\"");
String frenchConverted = convertToFrench(englishWordsReply);
System.out.println("John Converted " + "\"" + englishWordsReply + "\"" + " to " + "\""
               + frenchConverted + "\"" + " and send back to Rohit\n");
return frenchConverted;

}
else if( convertToWhichLanguage.equalsIgnoreCase("French") )

{
String frenchWords = convertToFrench(words);
System.out.println("\nJohn Converted \"" + words + " \" to \"" + frenchWords
               + " and send the question to Rohit");
String frenchWordsReply =rohit.answerFortheQuestion(frenchWords);
System.out.println("John Got reply from Rohit in French like : " + "\"" + frenchWordsReply
               + "\"");
String englishConverted = convertToEnglish(frenchWordsReply);
System.out.println("John Converted " + "\"" + frenchWordsReply + "\"" + " to " + "\""
               + englishConverted + "\"" + " and send back to David\n");
return englishConverted;

}

return "Sorry Cannot Covert";
}

public String convertToFrench( String words )
{
return englishFrenchMap.get(words);
}

public String convertToEnglish( String words )
{
return frenchEnglishMap.get(words);
}

}

EnglishSpeaker.java

public interface EnglishSpeaker
{
public String askQuestion( String words );
public String answerFortheQuestion( String words );

}

David.java

/*

 * He is from USA, So he can speak and understand only English

 */

public class David implements EnglishSpeaker

{

public static void main( String args[] )

{

String replyFromRohit = new David().askQuestion("how are you?");

System.out.println("Reply From Rohit [French Speaker can Speak and Understand only French] :  " + replyFromRohit);

}

@Override

public String askQuestion( String words )

{

System.out.println("Question Asked by David [English Speaker and Can understand only English] : " +words);

ITarget target = new John();

String replyFromRohit = target.translateAndTellToOtherPerson(words, "French");

return replyFromRohit;

}

@Override

public String answerFortheQuestion( String words )

{

String reply = null;

if( words.equalsIgnoreCase("where are you?") )

{

reply = "I am in USA";

}

return reply;

}

}

FrenchSpeaker.java

public interface FrenchSpeaker

{

public String askQuestion( String words );

public String answerFortheQuestion( String words );

}

Rohit.java

/*
 * He is from France, So he can speak and understand only French
 */
public class Rohit implements FrenchSpeaker
{

public static void main( String args[] )
{
String replyFromDavid = new Rohit().askQuestion("où êtes-vous?");
System.out.println("Reply From David [English Speaker can Speak and Understand only English] :  " + replyFromDavid);
}

@Override
public String askQuestion( String words )
{
System.out.println("Question Asked by Rohit [French Speaker and Can understand only French] : " +words);
ITarget target = new John();
String replyFromDavid = target.translateAndTellToOtherPerson(words, "English");
return replyFromDavid;
}

@Override
public String answerFortheQuestion( String words )
{
String reply = null;
if( words.equalsIgnoreCase("comment allez-vous?") )
{
reply = "Je suis très bien";
}
return reply;
}

}

Output

David asks Question to Rohit

Question Asked by David [English Speaker and Can understand only English] : how are you?

John Converted "how are you? " to "comment allez-vous? and send the question to Rohit
John Got reply from Rohit in French like : "Je suis très bien"
John Converted "Je suis très bien" to "I am fine" and send back to David

Reply From Rohit [French Speaker can Speak and Understand only French] :  I am fine

Rohit asks Question to David

Question Asked by Rohit [French Speaker and Can understand only French] : où êtes-vous?

John Converted "où êtes-vous? " to "where are you? and send the question to David
John Got reply from David in English like : "I am in USA"
John Converted "I am in USA" to "Je suis aux Etats-Unis" and send back to Rohit

Reply From David [English Speaker can Speak and Understand only English] :  Je suis aux Etats-Unis

See also:

Adapter Design pattern - Introduction

Adapter Design Pattern - Real Time Exmaple(Translator)

Adapter Design pattern - Real Time Example (Card Reader)

Adapter Design pattern - Real Time Example (Mobile Charger)

Adapter Design pattern - Real Time Example (Universal Adaptor)

Adapter Design pattern - Real Time Example [JDBC Driver]

Adapter Design pattern - Class diagram

Adapter Design Pattern - Sequence diagram

Adapter Pattern - Implementation [Object Adapter]

Adapter Pattern - Implementation [Class Adapter]

Adapter Design Pattern - Implementation [Mobile Charger]

Adapter Design Pattern - Key Points

All Design Patterns Links