Design Patterns#6 Adapter Pattern

Design Patterns

The Adapter Pattern is a structural design pattern that allows objects with incompatible interfaces to work together. It acts as a bridge between two incompatible interfaces, making them compatible without changing their source code. This pattern is especially useful when integrating new functionality or libraries into an existing system.

Here’s a simple example of the Adapter Pattern in Java:

Suppose you have an existing class OldSystem with a method legacyOperation():

class OldSystem {
    void legacyOperation() {
        System.out.println("Legacy operation is performed.");
    }
}

You want to use this OldSystem in a new system that expects an interface called NewSystemInterface with a method newOperation():

interface NewSystemInterface {
    void newOperation();
}

To make OldSystem compatible with the new system, you can create an adapter class that implements the NewSystemInterface and delegates calls to OldSystem's legacyOperation() method:

class OldSystemAdapter implements NewSystemInterface {
    private OldSystem oldSystem;

    OldSystemAdapter(OldSystem oldSystem) {
        this.oldSystem = oldSystem;
    }

    @Override
    public void newOperation() {
        oldSystem.legacyOperation();
    }
}

Now, you can use the OldSystem in your new system by creating an instance of the adapter:

public class Main {
    public static void main(String[] args) {
        OldSystem oldSystem = new OldSystem();
        NewSystemInterface adapter = new OldSystemAdapter(oldSystem);

        // The new system can use the old system through the adapter.
        adapter.newOperation();
    }
}

In this example, the OldSystemAdapter acts as a bridge between the old system's interface (OldSystem) and the new system's interface (NewSystemInterface). This allows the new system to call newOperation() on the adapter, which, in turn, delegates the call to the legacyOperation() method of the OldSystem class. This way, the incompatible interfaces are made compatible through the adapter, allowing them to work together seamlessly.

Prev: Design Patterns#5 Builder Pattern

Next: Design Patterns#7 Bridge Pattern