Walkthrough - Kotlin Tour: Properties

In this lesson, we explored how Kotlin manages data through properties. We covered backing fields, custom accessors, extension properties, and the powerful delegation model including lazy and observable.

Changes Made

Implementation

• Created Properties.kt which implements:
  • Backing Fields: Using the field keyword in a custom setter to format strings.
  • Extension Properties: Adding a fullName property to a data class without modifying its source.
  • Delegated Properties: A custom CachedStringDelegate to demonstrate manual delegation logic.
  • Lazy Properties: Using by lazy for thread-safe, deferred initialization (Database example).
  • Observable Properties: Using Delegates.observable to trigger logic on value changes (Thermostat example).
  • Exercises:
    • List indices for out-of-stock items.
    • Double.asMiles extension property.
    • Lazy health checks for system monitoring.
    • Budget tracker with thresholds using observables.
• Updated App.java to execute these demonstrations.

Verification

• Build: Successfully executed ./gradlew :app:assemble.
• Logic: Verified that field prevents infinite recursion and that lazy initialization only happens once.

See the Step-by-Step Explanation for technical details.