Definition of java8 function expression [definition of a LAMBDA expression]

English from: Java In a nutshell, 6th Edition

Definition of a Lambda Expression
A lambda expression is essentially a function of does not having a name, and can be
Treated as a value in the language. As Java does not allow code to run around in its
Own outside of classes, in Java, this means, a lambda was an anonymous method
That's defined on some class (that's possibly unknown to the developer).
-java In a nutshell, 6th Edition

In fact, a regular expression is a function without a name (parameter, return value, function body), which is considered a value in the Java language.
Because Java functions must be defined in a class, this means that a function expression in the Java language is an anonymous method defined in a class.

The function expression is treated as a value in Java, that is: Runnable r = (), System.out.println ("Hello World"); Form

Definition of java8 function expression [definition of a LAMBDA expression]