Closures and Variable Capture
Explore how Java lambdas form closures by capturing variables from their surrounding scope. Understand the effectively final rule that restricts modification of local variables to ensure consistent behavior and memory safety. Learn the difference between capturing mutable references and variables, and see why lambdas differ from anonymous inner classes in scope handling, enabling you to write cleaner, context-aware functional code in Java.
In the previous lesson, we treated functions as isolated units of logic. But in real-world software, functions often need context, configuration settings, user-defined thresholds, or running totals that exist outside the function itself.
In functional programming, when a function captures state from its surrounding environment, we call it a closure. Java lambdas support this feature, allowing us to write flexible, context-aware code. In this lesson, we will learn how to access external data safely from within a lambda and understand the rules Java enforces to keep these interactions predictable.
Capturing local variables
A lambda expression can use variables defined in the method where the lambda is created. This process is called variable capture. It allows us to dynamically configure a lambda’s behavior without having to pass every piece of data as a parameter.
Consider a scenario where we want to filter a list of prices, but the maximum price limit is determined by user input or a calculation earlier in the method. We don’t need to hardcode the limit; the lambda can simply “read” the local ...