Why Java interop matters in Kotlin - See It in Action

Why Java interop matters

📖 Scenario: You are building a Kotlin app that needs to use a Java library for handling dates. This is common because many Java libraries exist and Kotlin can use them directly.

🎯 Goal: Learn how to create a Kotlin variable, set a Java class instance, call a Java method, and print the result. This shows how Kotlin and Java work together smoothly.

📋 What You'll Learn

Create a Kotlin variable holding a Java java.util.Date object

Create a Kotlin variable called currentTime that stores the current time in milliseconds from the Java Date object

Use Kotlin to call the Java method getTime() on the Date object

Print the currentTime value

💡 Why This Matters

🌍 Real World

Many Kotlin apps use existing Java libraries for features like date handling, networking, or UI components.

💼 Career

Understanding Java interop is key for Kotlin developers working in Android or backend environments where Java codebases exist.

1

Create a Java Date object in Kotlin

Write a Kotlin line to create a variable called date that holds a new java.util.Date() object.

Kotlin

# Create a variable called date holding a new java.util.Date() object
# Your code here

Need a hint?

Use val date = java.util.Date() to create the Date object.

2

Get current time from the Date object

Create a Kotlin variable called currentTime and set it to the result of calling date.getTime().

Kotlin

val date = java.util.Date()
# Create currentTime by calling date.getTime()
# Your code here

Need a hint?

Use val currentTime = date.time to get the time in milliseconds.

3

Print the current time

Write a Kotlin println statement to display the value of currentTime.

Kotlin

val date = java.util.Date()
val currentTime = date.time
# Print currentTime
# Your code here

Need a hint?

Use println(currentTime) to show the time.

4

Run and observe Java interop in action

Run the program to see the current time in milliseconds printed. This shows Kotlin calling Java code smoothly.

Kotlin

val date = java.util.Date()
val currentTime = date.time
println(currentTime)
# Run the program and observe output

Need a hint?

The output should be a number showing the current time in milliseconds.