Do Java 8 Lambda Expressions Create a New Object for Each Iteration?

Performance Implications of Lambda Expressions in Java 8

When iterating over a collection using the stream API in Java 8, the new syntactic sugar introduced lambda expressions. However, the question arises: "Does this result in the creation of an anonymous Consumer object on the heap for each iteration?"

Does a Lambda Create a New Object on the Heap Every Time?

The answer is "no," but it's not quite as simple as that. If a lambda expression does not capture any values, it essentially becomes a singleton that is reused for every invocation.

JVM Implementation Details

The Java Virtual Machine (JVM) has flexibility in implementing lambda expressions. Oracle's JVM currently creates at least one instance per lambda expression but creates singletons for expressions that don't capture values.

Performance Implications

This behavior has performance implications for memory consumption and execution time:

• Memory Consumption: While lambdas may not create new objects every time, they still take up heap space. However, for simple lambdas without value capture, this overhead is typically minimal.
• Execution Time: The overhead of lambda execution is generally negligible, especially in comparison to the time spent processing the collection elements themselves.

When to Use the Old Style For Loop

It's generally recommended to use lambda expressions for iterating over collections because they provide concise and readable code. For extremely large multi-level data structures, where performance is critical, you may consider using traditional for loops. However, the performance difference is likely to be minor unless the data structure is truly massive.

The Java Language Specification

The behavior of lambda expressions is covered in The Java® Language Specification, chapter "15.27.4. Run-time Evaluation of Lambda Expressions." It allows for flexibility in implementation, allowing the JVM to optimize memory usage and execution time.

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