Scalable Human Blog

With the release of Java 8, a new feature called “Default Methods” was introduced to Java interfaces. This powerful feature has significantly influenced the way we design and utilize interfaces in Java. In this blog post, we’ll explore what default methods are, why they were introduced, and how we can effectively use them.

What are Default Methods?

Before Java 8, interfaces in Java could only declare method signatures. However, with the introduction of default methods, interfaces can now also contain method implementations. A default method in an interface is defined using the default keyword before the method signature. Here’s an example:

public interface Animal

{

void eat();

default void breathe() {

System.out.println("Breathing...");

}

}

In this example, breathe is a default method. It provides a common default behavior that can be used by any class implementing the Animal interface.

Why were Default Methods introduced?

One of the primary reasons for introducing default methods was to enhance the Java Collections API for the Lambda expressions feature introduced in Java 8. It allows adding non-abstract method implementations to interfaces without breaking the existing implementations of these interfaces.

Before Java 8, if a new method was to be added in an interface, then it had to be implemented in all classes that use this interface. With default methods, this constraint is removed, and interfaces became more flexible.

Using Default Methods

When a class implements the Animal interface:

public class Dog implements Animal {

@Override public void eat() {

System.out.println("Dog eating...");

}

}

The Dog class now has access to the breathe method:

Dog dog = new Dog();

dog.eat(); // Dog eating...

dog.breathe(); // Breathing...

Here, Dog can utilize the default breathe method without providing its own implementation.

Overriding Default Methods

Though the breathe method provides a default implementation, classes are free to override this behaviour:

public class Fish implements Animal {

@Override public void eat() {

System.out.println("Fish eating...");

}

@Override public void breathe() {

System.out.println("Fish breathing underwater...");

}

}

In this case, the Fish class overrides the breathe method to provide a different implementation:

Fish fish = new Fish();

fish.eat(); // Fish eating...

fish.breathe(); // Fish breathing underwater...

Conclusion

The introduction of default methods in Java 8 revolutionised interface design. By enabling interfaces to provide default method implementations, they introduced a degree of flexibility and functionality to interfaces that was not possible before. As we’ve seen, default methods allow us to extend interfaces without breaking existing implementations, thus aiding in software evolution. As always, while powerful, this feature should be used judiciously to maintain clean and understandable code.

📚 Further Reading & Related Topics

If you’re exploring Java interfaces and default methods, these related articles will provide deeper insights into Java’s evolving language features:

• Java 13 and the Evolution of Switch Expressions: A Deeper Dive – Learn how Java continues to enhance readability and flexibility with improved control flow structures, much like default methods improve interface design.

• Java 16 and the Standardization of Records: Simplifying Data Classes – Explore how Java records complement default methods by offering a modern approach to defining immutable data structures.