Does a lambda expression create an object on the heap every time it's executed?

Question

When I iterate over a collection using the new syntactic sugar of Java 8, such as

myStream.forEach(item -> {
  // do something useful
});

<

Answer 1

When an instance representing the lambda is created sensitively depends on the exact contents of your lambda's body. Namely, the key factor is what the lambda captures from the lexical environment. If it doesn't capture any state which is variable from creation to creation, then an instance will not be created each time the for-each loop is entered. Instead a synthetic method will be generated at compile time and the lambda use site will just receive a singleton object that delegates to that method.

Further note that this aspect is implementation-dependent and you can expect future refinements and advancements on HotSpot towards greater efficiency. There are general plans to e.g. make a lightweight object without a full corresponding class, which has just enough information to forward to a single method.

Here is a good, accessible in-depth article on the topic:

http://www.infoq.com/articles/Java-8-Lambdas-A-Peek-Under-the-Hood