Platform types and null safety in Kotlin - Mini Project: Build & Apply

Platform types and null safety

📖 Scenario: You are working on a Kotlin app that interacts with Java code. Java methods can return values that might be null, but Kotlin needs you to handle nulls safely.This project will help you understand how Kotlin treats platform types from Java and how to use null safety features to avoid crashes.

🎯 Goal: Build a Kotlin program that calls a Java method returning a platform type, then safely handles possible null values using Kotlin's null safety features.

📋 What You'll Learn

Create a Kotlin variable to hold a platform type value returned from a Java method

Create a nullable Kotlin variable to hold the same value safely

Use a safe call operator to access the length of the string safely

Print the length or a message if the value is null

💡 Why This Matters

🌍 Real World

Many Kotlin apps use Java libraries. Understanding platform types helps avoid crashes from unexpected nulls.

💼 Career

Handling null safety and platform types is essential for Kotlin developers working with mixed Java-Kotlin codebases.

1

Create a Kotlin variable with a platform type value

Create a Kotlin variable called platformString and assign it the value returned by the Java method JavaClass.getPlatformString().

Kotlin

class JavaClass {
    companion object {
        @JvmStatic
        fun getPlatformString(): String? = null
    }
}

fun main() {
    // Create platformString variable assigned from JavaClass.getPlatformString()
    // Your code here
}

Need a hint?

Use val platformString = JavaClass.getPlatformString() to get the platform type value.

2

Create a nullable Kotlin variable to hold the platform type safely

Create a nullable Kotlin variable called safeString and assign it the value of platformString.

Kotlin

class JavaClass {
    companion object {
        @JvmStatic
        fun getPlatformString(): String? = null
    }
}

fun main() {
    val platformString = JavaClass.getPlatformString()
    // Create nullable variable safeString assigned from platformString
    // Your code here
}

Need a hint?

Declare safeString as nullable String and assign platformString to it.

3

Use safe call operator to get length safely

Create a variable called length and assign it the length of safeString using the safe call operator ?..

Kotlin

class JavaClass {
    companion object {
        @JvmStatic
        fun getPlatformString(): String? = null
    }
}

fun main() {
    val platformString = JavaClass.getPlatformString()
    val safeString: String? = platformString
    // Create length variable using safe call operator on safeString
    // Your code here
}

Need a hint?

Use safeString?.length to get length safely without errors if null.

4

Print the length or a message if null

Print the value of length if it is not null; otherwise, print "Length is unknown" using the Elvis operator ?:.

Kotlin

class JavaClass {
    companion object {
        @JvmStatic
        fun getPlatformString(): String? = null
    }
}

fun main() {
    val platformString = JavaClass.getPlatformString()
    val safeString: String? = platformString
    val length = safeString?.length
    // Print length or "Length is unknown" if length is null
    // Your code here
}

Need a hint?

Use println(length ?: "Length is unknown") to print length or fallback message.