Functions vs classes
Bear in mind that an anonymous function isn't the same as an anonymous class in Java. An anonymous class in Java still needs to be instantiated to an object. It may not have a proper name, but it can be useful only when it's an object.
A function on the other hand has no instance associated with it. Functions are disassociated with the data they act on whereas an object is intimately associated with the data it acts upon.
You can use lambdas in modern Java anywhere you would have previously used a single method interface so it may just look like syntactic sugar but it's not. Let's have a look at how they differ and compare anonymous classes to lambdas; classes vs. functions.
Lambdas in modern Java
A typical implementation of an anonymous class (a single method interface) in Java pre-8, might look something like this. The anonymousClass method is calling the waitFor method, passing in some implementation of Condition; in this case, it's saying, wait for some server to shutdown...
