Do method references skip the overhead of the lambda wrapper? Might they in the future?
According to the Java Tutorial on Method References:
Sometimes... a lambda expression does nothing but call an existing method. In those cases, it's often clearer to refer to the existing method by name. Method references enable you to do this; they are compact, easy-to-read lambda expressions for methods that already have a name.
I prefer the lambda syntax to the method reference syntax for several reasons:
Lambdas are clearer
Despite Oracle's claims, I find the lambda syntax easier-to-read than the object method reference short-hand because the method reference syntax is ambiguous:
Are you calling a static one-argument method on the class of x and passing it x?
x -> Bar.foo(x)
Or are you calling a zero-argument instance method on x?
x -> x.foo()
The method reference syntax could stand in for either one. It hides what your code is actually doing.
Lambdas are safer
If you reference Bar::foo as a class method and Bar later adds an instance method of the same name (or vice-versa), your code will no longer compile.
You can use lambdas consistently
You can wrap any function in a lambda - so you can use the same syntax consistently everywhere. The method reference syntax won't work on methods that take or return primitive arrays, throw checked exceptions, or have the same method name used as an instance and a static method (because the method reference syntax is ambiguous about which method would be called). They don't work when you have overloaded methods with the same number of arguments, but you shouldn't do that anyway (see Josh Bloch's item 41) so we can't hold that against method references.
If there's no performance penalty for doing so, I'm tempted to turn off the warning in my IDE and use the lambda syntax consistently without sprinkling the occasional method reference into my code.
Neither here nor there, but in my dreams, object method references look more like this and apply invoke-dynamic against the method directly on the object without a lambda wrapper: