Wrapper
Convert the interface of a class into another interface the clients expect. Adapter lets classes work together that couldn’t otherwise because of incompatible interfaces.
Real-world example
Consider that you have some pictures on your memory card and you need to transfer them to your computer. To transfer them, you need some kind of adapter that is compatible with your computer ports so that you can attach a memory card to your computer. In this case card reader is an adapter. Another example would be the famous power adapter; a three-legged plug can’t be connected to a two-pronged outlet, it needs to use a power adapter that makes it compatible with the two-pronged outlets. Yet another example would be a translator translating words spoken by one person to another
In plain words
Adapter pattern lets you wrap an otherwise incompatible object in an adapter to make it compatible with another class.
Wikipedia says
In software engineering, the adapter pattern is a software design pattern that allows the interface of an existing class to be used as another interface. It is often used to make existing classes work with others without modifying their source code.
Programmatic Example
Consider a captain that can only use rowing boats and cannot sail at all.
First, we have interfaces RowingBoat
and FishingBoat
1public interface RowingBoat {
2 void row();
3}
4
5@Slf4j
6public class FishingBoat {
7 public void sail() {
8 LOGGER.info("The fishing boat is sailing");
9 }
10}
And captain expects an implementation of RowingBoat
interface to be able to move
1public class Captain {
2
3 private final RowingBoat rowingBoat;
4 // default constructor and setter for rowingBoat
5 public Captain(RowingBoat rowingBoat) {
6 this.rowingBoat = rowingBoat;
7 }
8
9 public void row() {
10 rowingBoat.row();
11 }
12}
Now let’s say the pirates are coming and our captain needs to escape but there is only a fishing boat available. We need to create an adapter that allows the captain to operate the fishing boat with his rowing boat skills.
1@Slf4j
2public class FishingBoatAdapter implements RowingBoat {
3
4 private final FishingBoat boat;
5
6 public FishingBoatAdapter() {
7 boat = new FishingBoat();
8 }
9
10 @Override
11 public void row() {
12 boat.sail();
13 }
14}
And now the Captain
can use the FishingBoat
to escape the pirates.
1var captain = new Captain(new FishingBoatAdapter());
2captain.row();
Use the Adapter pattern when
Class and object adapters have different trade-offs. A class adapter
An object adapter