?? Java Lambdas: Why They Work with Single-Method Interfaces ??

If you've worked with Java lambdas, you may have wondered: Why do lambdas only work with Single Abstract Method (SAM) interfaces? Here’s a simple way to understand it!

?? Real-Life Example

Imagine you're ordering coffee at a cafe. The barista only asks, "What drink would you like?" You respond, "A latte, please!"

The interaction is simple because there's only one question for you to answer. Now, imagine if the barista asked multiple questions at once (like your favorite song, today’s weather, and your coffee choice). The conversation would become confusing, right? ??

In the same way, Java lambdas are designed to answer only one question — they’re meant to define one specific behavior, like “run” or “compare.”

?? In Code

Java uses Single Abstract Method (SAM) interfaces for this exact reason. These interfaces have only one method to implement, making it super clear what behavior the lambda is defining. Here’s how it looks:

List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
names.forEach(name -> System.out.println("Hello, " + name));        

In this example, name -> System.out.println("Hello, " + name) is a lambda expression implementing a Consumer interface (which has only one method: accept()). Java knows exactly what we want to do here — print each name with a greeting — just like when the barista asks for your drink order.

?? Why Only SAM Interfaces?

If interfaces had more than one method, Java wouldn’t know which one to use, just like the barista asking too many questions at once. Using SAM interfaces keeps things clear, simple, and straightforward for lambdas.

This design keeps Java code clean and easy to read. If you’ve used lambdas in Java, let’s chat about how they’ve simplified your coding experience! ??

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