這篇文章將幫助您了解Java 8中一些重要且經(jīng)常使用的Stream操作，這使您使用Java編程變得容易。

讓我們以傳統(tǒng)示例為例，“員工和部門”。

public class Employee {private String name;private Integer age;private String city;private Department department;public Employee(String name, Integer age, String city, Department department) {this.name = name;this.age = age;this.city = city;this.department = department;}// getters and setters.}public class Department {private String departmentName;private Integer noOfEmployees;public Department(String departmentName, Integer noOfEmployees) {this.departmentName = departmentName;this.noOfEmployees = noOfEmployees;}// getters and setters }

我將按如下所示設(shè)置一些示例數(shù)據(jù)，以便向您展示Java 8 Stream接口的一些重要功能。 我們有四個(gè)部門，以及來自這些部門的一組員工。

Department account = new Department("Account", 75); Department hr = new Department("HR", 50);Department ops = new Department("OP", 25);Department tech = new Department("Tech", 150); List<Employee> employeeList = Arrays.asList(new Employee("David", 32, "Matara", account), new Employee("Brayan", 25, "Galle", hr),new Employee("JoAnne", 45, "Negombo", ops),new Employee("Jake", 65, "Galle", hr),new Employee("Brent", 55, "Matara", hr),new Employee("Allice", 23, "Matara", ops),new Employee("Austin", 30, "Negombo", tech),new Employee("Gerry", 29, "Matara", tech),new Employee("Scote", 20, "Negombo", ops),new Employee("Branden", 32, "Matara", account),new Employee("Iflias", 31, "Galle", hr));

查找所有居住在“ Matara”城市的員工，按姓名對(duì)他們進(jìn)行排序，然后打印員工的姓名。

employeeList.stream().filter(e -> e.getCity().equalsIgnoreCase("Matara")).sorted(Comparator.comparing(Employee::getName)).forEach(e -> System.out.println(e.getName()));

查找員工工作的不同部門名稱。

employeeList.stream().map(e -> e.getDepartment().getDepartmentName()).distinct().forEach(System.out::println);

查找這些員工所在的部門名稱，該部門的員工人數(shù)超過50。

employeeList.stream().map(Employee::getDepartment).filter(d -> d.getNoOfEmployees() > 50).distinct().forEach(d -> System.out.println(d.getDepartmentName()));

創(chuàng)建一個(gè)逗號(hào)分隔的部門名稱字符串，按字母順序排序。

String s = employeeList.stream().map(e -> e.getDepartment().getDepartmentName()).distinct().sorted().reduce("", (a, b) -> (a + "," + b)); System.out.println(s);

人力資源部有員工嗎？

if (employeeList.stream().anyMatch(e -> e.getDepartment().getDepartmentName().equalsIgnoreCase("HR"))) { System.out.println("Found employees frm HR department"); }

打印在會(huì)計(jì)部門工作的所有雇員的姓名。

employeeList.stream().filter(e -> e.getDepartment().getDepartmentName().equalsIgnoreCase("Account")).map(Employee::getName).forEach(System.out::println);

所有部門的最高員工人數(shù)是多少？

employeeList.stream().map(e -> e.getDepartment().getNoOfEmployees()).reduce(Integer::max).ifPresent(System.out::print);

查找員工人數(shù)最多的部門。

employeeList.stream().map(Employee::getDepartment).reduce( (d1, d2) -> d1.getNoOfEmployees() > d2.getNoOfEmployees() ? d1 : d2).ifPresent(d -> System.out.println(d.getDepartmentName()));

使用max（）方法可以完成以下相同操作。

employeeList.stream().map(Employee::getDepartment).max(Comparator.comparing(Department::getNoOfEmployees)).ifPresent(d -> System.out.println(d.getDepartmentName()));

查找所有部門的員工總數(shù)。

employeeList.stream().map(e -> e.getDepartment().getNoOfEmployees()).distinct().reduce(Integer::sum).ifPresent(System.out::println);

翻譯自: https://www.javacodegeeks.com/2018/07/java-8-stream-examples.html

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