Java™ How To Program (Early Objects), Tenth Edition

17.6.3 Sorting Employees By Multiple Fields

Figure 17.12 shows how to use streams to sort objects by multiple fields. In this example, we sort Employees by last name, then, for Employees with the same last name, we also sort them by first name. To do so, we begin by creating two Functions 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 method getLastName

Next, we use these Functions to create a Comparator (lastThenFirst; lines 58–59) that first compares two Employees by last name, then compares them by first name. We use Comparator method comparing to create a Comparator ...