Custom Interfaces

Details about custom functional interfaces in Java.

Custom functional interfaces are interfaces in Java that extend the functionalities of the built-in functional interfaces (like Function, Predicate, etc.) to fit specific needs within the application. They adhere to the principle of having exactly one abstract method.

Benefits:

• Improved code organization: Encapsulates specific functionalities, making code more organized and easier to understand.

• Enhanced reusability: Allows to reuse the same interface for different implementations, promoting code reusability.

• Flexibility: Enables you to create interfaces that cater to specific needs not directly addressed by the built-in options.

Example:

Lets create a custom functional interface class.

@FunctionalInterface
public interface StringModifier {
    String modify(String str);
}

Now, implement the Interface. There are two ways to implement this interface.

• Using a separate class

public class UppercaseModifier implements StringModifier {

    @Override
    public String modify(String str) {
        return str.toUpperCase();
    }
}

• Using a Lambda Expression

StringModifier lowercaseModifier = str -> str.toLowerCase();

Then use the interface

String originalString = "Hello World!";

// Using separate class implementation
StringModifier uppercaseModifier = new UppercaseModifier();
String uppercaseString = uppercaseModifier.modify(originalString);
log.info(uppercaseString); 
// Output: HELLO WORLD!

// Using lambda expression
String lowercaseString = lowercaseModifier.modify(originalString);
log.info(lowercaseString); 
// Output: hello world!