Lambda Expressions - Java 8 Recipes - page 221

one of the standard functional interfaces contained within the
java.util.function package (see Recipe 6-2), and the interface can be imple-
mented by lambda expressions and then invoked at a later time by calling its solo ap-
ply() method. Looking at the code in the calculate() method, the arguments
contained within the Double[] are first added to a list. Next, lambda expression's
apply() method is invoked, passing the new list of values, and returning a result into
returnVal . Finally, returnVal is returned to the method invoker.
returnVal=f1.apply(varList);
return returnVal;
To implement the calculation functionality within the solution, lambda expressions
are created in a separate class named MainClass . Each expression accepts a list of
arguments and then performs a calculation on the values in the list, returning a result.
For instance, the first lambda generated in the MainClass calculates volume by mul-
tiplying together all of the values contained in the argument list and returns the result.
This functionality is then assigned to a variable of type Func-
tion<List<Double>,Double> , and then it is passed into the
PassingLambdaFunctions.calculate() method later on.
Any type of functionality can be implemented within a lambda expression and then
passed around to different objects for use. This is an excellent way to promote code re-
use and high maintainability.
6-9. Invoking Existing Methods by Name
Problem
You are developing a lambda expression that merely invokes a method that already ex-
ists in the object being passed to the lambda.
Solution
Use a method reference, rather than writing a lambda expression, to call an existing
method. In the following scenario, the Player object contains a static method named
compareByGoals() , which takes two Player objects and compares the number
of goals each contains. It then returns an integer representing the outcome. For all in-