Function.identity() vs. str->str: When Should You Choose Which?

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Function.identity() vs. str->str in Java 8 Lambdas

The Function.identity() method in Java 8 provides a convenient way to represent an identity function, which simply returns its input value. This raises the question: why use Function.identity() instead of the more concise str->str syntax?

Implementation Differences

Despite their similar functionality, Function.identity() and str->str differ in their implementation. Function.identity() returns the same instance every time it is called, while each instance of str->str creates a new implementation class.

This distinction becomes evident in debugging scenarios. With Function.identity(), the line debug attribute points to the source code line of the lambda expression. However, for instances returned by Function.identity(), this information is not available.

Memory Considerations

Function.identity() is a statically declared method, while str->str creates a new object for each lambda expression. As a result, using Function.identity() can save memory in certain cases.

Readability

Ultimately, the choice between Function.identity() and str->str comes down to readability and preference. Some developers may find str->str to be more concise and easier to understand, while others may prefer the explicit representation of identity provided by Function.identity().

Conclusion

While the syntax of Function.identity() and str->str is similar, they exhibit different implementation details. Function.identity() provides a static instance with debugging benefits, while str->str generates unique instances with the potential for readability improvements. The choice between these options is based on memory considerations, readability preferences, and debugging needs.

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