Do Java 8 Lambda Expressions Always Create New Heap Objects?

Lambda Expression Performance: Heap Allocation and Instance Creation

When utilizing Java 8's lambda syntax to iterate over collections, a common concern arises: does each lambda invocation create a new object on the heap? Is it comparable to the traditional syntax using anonymous classes?

Answer:

Yes and no. While lambda expressions are functionally equivalent to anonymous classes, they exhibit different implementation behaviors.

Specifically, lambda expressions that do not capture values (i.e., they do not access variables outside their scope) become singletons that are reused across invocations. This means they do not create a new object on the heap each time.

However, if a lambda expression captures values, a new instance is created for each execution. The JVM's implementation determines the exact behavior, but Oracle's JVM currently creates singletons for value-capturing lambdas and instantiates multiple instances for non-singletons.

Heap Space and Performance Implications:

Singletons optimize heap space utilization, as only a single instance is allocated regardless of how many times the lambda is executed. For value-capturing lambdas, however, multiple instances can consume significant heap space, especially when used frequently.

Furthermore, creating new instances on each invocation introduces a performance penalty. For value-capturing lambdas with complex logic or capturing large variables, the performance overhead can be noticeable.

Recommendations:

Whether to favor lambda expressions or traditional for loops depends on the nature of the lambda expression. Singletons provide performance advantages, while value-capturing lambdas may incur heap space and performance costs. For large multi-level data structures, traditional for loops may be more appropriate if performance is critical.

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