Using the Adapter Design Pattern in Java

Here I am with another useful design pattern for you — the adapter design pattern. I will also highlight the differences between the decorator design pattern (see my previous article, Decorator Design Pattern in Java, here) and the adapter design pattern.

Adapter Design Pattern

• The adapter design pattern is a structural design pattern that allows two unrelated/uncommon interfaces to work together. In other words, the adapter pattern makes two incompatible interfaces compatible without changing their existing code.
• Interfaces may be incompatible, but the inner functionality should match the requirement.
• The adapter pattern is often used to make existing classes work with others without modifying their source code.
• Adapter patterns use a single class (the adapter class) to join functionalities of independent or incompatible interfaces/classes.
• The adapter pattern also is known as the wrapper, an alternative naming shared with the decorator design pattern.
• This pattern converts the (incompatible) interface of a class (the adaptee) into another interface (the target) that clients require.
• The adapter pattern also lets classes work together, which, otherwise, couldn’t have worked, because of the incompatible interfaces.
• For example, let’s take a look at a person traveling in different countries with their laptop and mobile devices. We have a different electric socket, volt, and frequency measured in different countries and that makes the use of any appliance of one country to be freely used in a different country. In the United Kingdom, we use Type G socket with 230 volts and 50 Hz frequency. In the United States, we use Type A and Type B sockets with 120 volts and 60 Hz frequency. In India, we use Type C, Type D. and Type M sockets with 230 volts and 50 Hz. lastly, in Japan, we use Type A and Type B sockets with 110 volts and 50 Hz frequency. This makes the appliances we carry incompatible with the electric specifications we have at different places.
• This makes the adapter tool essential because it can make/convert incompatible code into compatible code. Please notice here that we have not achieved anything additional here — there is no additional functionality, only compatibility.

To better understand this, let’s look at an example of geometric shapes. I am keeping the example relatively simple to keep the focus on the pattern. Suppose we have a project of drawing, in which we are required to develop different kinds of geometric shapes that will be used in the Drawing via a common interface called  Shape.

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