Lambda Expressions - Java 8 Recipes - page 209

In solution 1, a Comparator is generated, by which the Player objects will be
evaluated for the number of goals scored ( getGoals ). A stream is then generated
from a List<Player> that is referenced as team. The stream provides the sor-
ted() function, which accepts a Comparator by which to perform a sort on a
stream of data. The Comparator that was initially generated is passed to the sor-
ted() function, and then the map() function is called upon the result. The map()
function provides the ability to map expressions to each element within the stream.
Therefore, within the map, this solution utilizes a lambda expression to create a string
that contains each Player object's firstName , lastName , and goals fields.
Lastly, since the List<Player> is an iterable, it contains the forEach() method.
The forEach() method enables an expression or group of statements to be applied
to each element within the list. In this case, each element in the list is printed to the
command line. As such, since the map() function was applied to the stream, each ele-
ment in the list is subsequently printed per the algorithm applied within the map() .
Therefore, the result is that the players first and last names along with the number of
goals each has scored will be printed at the command line.
Solution 2 uses a different technique to accomplish a similar task. In the second
solution, the Collections.sort() method is invoked on the list. The first argu-
ment to Collections.sort() is the list itself, and the second argument is the
comparison implementation in the form of a lambda expression. The lambda expres-
sion in this case has two parameters passed to it, both Player objects, and it com-
pares the lastName of the first player to the lastName of the second player. There-
fore, the sort will be performed on the lastName field of the Player object, in as-
cending order. To finish off solution 2, the sorted list is printed out. To do this a stream
is generated from the sorted list, and the forEach() method is then invoked on the
stream of data, printing out each player's lastName .
No doubt, the lambda expression greatly reduces the amount of code required to
sort collections of data. It also makes it easy to understand the logic behind the sort, as
readability is much easier than trying to follow looping implementations of the past.
For more examples on using lambdas with collections of data, see Chapter 7 .
6-4. Specifying Filter Criteria on a Col-
lection of Data
Problem