How are lazy streams implemented in Java 8?

Question

I am reading Java 8, specifically the \"Streams API\". I wanted to know how streams can be lazy?

I believe streams are just added as a library and there are no chang

Answer 1

No reflection or proxies. Reflection and proxies come with a performance cost that should be avoided unless there isn't an alternative and performance is number one in Java.

What makes laziness possible is the functional style of doing things. Basically a stream starts with a source(ex: List), number of intermediate operations (ex: filters, map..) , and a terminal operation (ex: count, sum, etc..). Intermediate steps execute lazily because you pass functions (lambdas) that get chained in the pipeline to be executed at the terminal step.

ex: filter(Predicate)

filter in this example expects a function that tells us whether an object in the stream meets some criteria or not.

A lot of features that come from Java 7 have been used to make this efficient. Ex: invoke dynamic for executing lambdas rather than proxies or anonymous inner classes and ForkJoin pools for parallel execution.

If you are interested in Java 8 internals,then you have to watch this talk given by the expert in the field Brian Goetz, it's on Youtube.