这是获得预期结果的方法之一

List<String> nameNickNameList = new ArrayList<String>();
        List<String> combinedList = new ArrayList<String>();
        // add all names to nameNickNameList 
        empList.stream().filter( e -> (nameNickNameList.add(e.getName()) )).collect(Collectors.toList()); 
        // add all nickNames to nameNickNameList 
        empList.stream().filter( e -> (nameNickNameList.add(e.getNickName()) )).collect(Collectors.toList());
        // filter out non null values and assign to combinedList 
        combinedList = nameNickNameList.stream().filter(s -> (s!=null) && !s.trim().isEmpty()).collect(Collectors.toList());

        for(String s : combinedList) {
            System.out.println(s);
        }

输入：emplist已

Employee e1 = new Employee("James","Jimmy", 20.5);
        Employee e2 = new Employee("Robert",null, 25.5);
        Employee e3 = new Employee("Kevin","Kev", 12.0);
        Employee e4 = new Employee("David","", 16.0);
        Employee e5 = new Employee("Alexander","Alex", 5.0);

输出

James
Robert
Kevin
David
Alexander
Jimmy
Kev
Alex