SAM conversions for Java interfaces in Kotlin - Mini Project: Build & Apply

SAM conversions for Java interfaces in Kotlin

📖 Scenario: You are working on a Kotlin project that uses a Java interface with a single abstract method (SAM). You want to use Kotlin's SAM conversion feature to simplify your code by passing a lambda instead of an anonymous class.

🎯 Goal: Learn how to use SAM conversions in Kotlin to implement a Java interface with a single abstract method using a lambda expression.

📋 What You'll Learn

Create a Java interface with a single abstract method

Create a Kotlin variable to hold an instance of the Java interface

Use a lambda expression to implement the interface using SAM conversion

Print the result of calling the interface method

💡 Why This Matters

🌍 Real World

SAM conversions let Kotlin developers write concise code when working with Java libraries that use interfaces with a single method, such as event listeners or callbacks.

💼 Career

Understanding SAM conversions is important for Kotlin developers working in mixed Java-Kotlin codebases, improving code readability and reducing boilerplate.

1

Create the Java interface

Create a Java interface called Action with a single abstract method perform that returns a String.

Kotlin

// Create the Java interface Action with method perform
// Your code here

Need a hint?

Remember, a Java interface with one method is a SAM interface.

2

Create a Kotlin variable for the interface

In Kotlin, create a variable called action of type Action and assign it null for now.

Kotlin

public interface Action {
    String perform();
}

// Create a Kotlin variable action of type Action and assign null
// Your code here

Need a hint?

Use val to declare a Kotlin variable and specify the type Action?.

3

Use SAM conversion with a lambda

Change the Kotlin variable action to use SAM conversion by assigning a lambda that returns the string "Action performed".

Kotlin

public interface Action {
    String perform();
}

// Assign a lambda to action using SAM conversion that returns "Action performed"
val action: Action = /* Your code here */

Need a hint?

Use Action { "Action performed" } to create the instance with SAM conversion.

4

Print the result of calling the interface method

Write a Kotlin println statement to print the result of calling perform() on the action variable.

Kotlin

public interface Action {
    String perform();
}

val action: Action = Action { "Action performed" }

// Print the result of action.perform()
// Your code here

Need a hint?

Call action.perform() inside println to display the message.