Closures and Variable Capture
Explore how Java lambdas capture and use external variables from their surrounding context, known as closures. Understand the effectively final rule for local variable capture, why immutability is required, and how this enables safe and consistent state management in functional programming. Learn the difference between mutable objects and references, and compare lambdas to anonymous inner classes for scope handling.
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 ...