使用Java8流如何使用一个列表获得两个不同的列表[重复]

Question

假设我有员工数据列表。

class Employee {
   private long id;
   private String name;
   private int age;
   // Constrctor
   // setters & getters
}
List<Employee> empList = ...;

使用上面的empList，如何获得两个不同的列表，如年龄

Answer 1

您可以执行以下操作：

List<Employee> greaterThan20 = empList.filter(e -> e.age > 20).collect(Collectors.toList());

List<Employee> lessThan20 = empList.filter(e -> e.age < 20).collect(Collectors.toList());

Answer 2

您可以使用Collectors.groupingBy

Map<Boolean, List<Employee>> ageGtThan20ToEmployees = empList.stream()
                .collect(Collectors.groupingBy(e -> e.age > 20));
System.out.println("Employees 20 years old are: "+ageGtThan20ToEmployees.get(true));

Answer 3

您可以使用收集器。分区依据

public static void main(String[] args) {
    List<Employee> employeeList = Arrays.asList(new Employee(10), new Employee(15),
            new Employee(21), new Employee(22));

    Map<Boolean, List<Employee>> employeeGroups = employeeList.stream().
                    collect(Collectors.partitioningBy(s -> s.getAge() > 20));

    System.out.println(employeeGroups.get(false));
    System.out.println(employeeGroups.get(true));
}

输出：

[Employee{age=10}, Employee{age=15}]
[Employee{age=21}, Employee{age=22}]