🔌Adapter Pattern – Overview

🧠 Concept

The Adapter Pattern allows incompatible interfaces to work together by providing a wrapper (adapter) that translates one interface into another.

💡 Think of it as a power plug converter — it adapts one type of plug to fit another socket.

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🧱 Key Roles

Role	Description
Target	The expected interface (what the client uses).
Adaptee	The existing class with an incompatible interface.
Adapter	Wraps the Adaptee and translates its interface into the Target’s format.
Client	Uses the Target interface — unaware of the adapter’s internal conversion.

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💻 Java Example – UI Example (Modern vs Legacy Buttons)

// ----- Target Interface -----
interface Button {
    void click();
}

// ----- Adaptee -----
class LegacyButton {
    public void onPress() {
        System.out.println("Legacy button pressed!");
    }
}

// ----- Adapter -----
class ButtonAdapter implements Button {
    private LegacyButton legacyButton;

    public ButtonAdapter(LegacyButton legacyButton) {
        this.legacyButton = legacyButton;
    }

    @Override
    public void click() {
        // Adapt click() call to legacy onPress() method
        legacyButton.onPress();
    }
}

// ----- Client -----
public class Main {
    public static void main(String[] args) {
        Button newButton = new ButtonAdapter(new LegacyButton());
        newButton.click();  // Client uses Target interface
    }
}

Output:

Legacy button pressed!

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🧠 Flow Summary

Step	Action	Adapter Does
1️⃣	Client calls click()	Adapter receives the call
2️⃣	Adapter translates click() → onPress()	Calls legacy method
3️⃣	Adaptee (LegacyButton) executes normally	Works seamlessly

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🪜 Summary

• Converts one interface to another that the client expects.

• Enables reuse of existing (legacy) classes with new systems.

• Promotes open/closed principle — extend behavior without modifying existing code.

• Can be implemented via object composition (preferred) or class inheritance.

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🧾 Real-world Analogy

🔌 Power Adapter

• Laptop (client) expects a USB-C plug (Target).

• Wall outlet has Type G plug (Adaptee).

• Adapter converts between them so they can connect.

💡 The devices stay unchanged — only the adapter bridges them.

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🧭 TL;DR

Adapter Pattern = Translator between incompatible interfaces. “Make old code talk to new code — without changing either.”