Java SE 8 Lambdas and Streams - Java: How to Program Early Objects - page 753

them by first name. To do so, we begin by creating two Function s that each receive an
Employee and return a String :
• byFirstName (line 54) is assigned a method reference for Employee instance
method getFirstName
• byLastName (line 55) is assigned a method reference for Employee instance meth-
od getLastName
Next, we use these Function s to create a Comparator ( lastThenFirst ; lines 58-59) that
first compares two Employee s by last name, then compares them by first name. We use
Comparator method comparing to create a Comparator that calls Function byLastName
on an Employee to get its last name. On the resulting Comparator , we call Comparator
method thenComparing to create a Comparator that first compares Employee s by last name
and, if the last names are equal , then compares them by first name. Lines 64-65 use this
new lastThenFirst Comparator to sort the Employee s in ascending order, then display the
results. We reuse the Comparator in lines 71-73, but call its reversed method to indicate
that the Employee s should be sorted in descending order by last name, then first name.

53 // Functions for getting first and last names from an Employee

54 Function<Employee, String> byFirstName = Employee::getFirstName;

Function<Employee, String> byLastName = Employee::getLastName; 55

56
57 // Comparator for comparing Employees by first name then last name

58 Comparator<Employee> lastThenFirst =

Comparator.comparing(byLastName).thenComparing(byFirstName); 59

60
61 // sort employees by last name, then first name

62 System.out.printf(

63 "%nEmployees in ascending order by last name then first:%n" );

64 list.stream()

65 .sorted(lastThenFirst)

66 .forEach(System.out::println);

67
68 // sort employees in descending order by last name, then first name

69 System.out.printf(

70 "%nEmployees in descending order by last name then first:%n" );

71 list.stream()

72 .sorted( lastThenFirst.reversed() )

73 .forEach(System.out::println);

74

Employees in ascending order by last name then first:
Jason Blue 3200.00 Sales
Wendy Brown 4236.40 Marketing
Ashley Green 7600.00 IT
James Indigo 4700.77 Marketing
Luke Indigo 6200.00 IT
Matthew Indigo 3587.50 Sales
Jason Red 5000.00 IT

Fig. 17.12 | Sorting Employee s by last name then first name. (Part 1 of 2.)