Java8新特性之Stream API详解

这篇文章主要介绍了Java8新特性之StreamAPI详解,文中有非常详细的代码示例,对正在学习java的小伙伴们有非常好的帮助,需要的朋友可以参考下

一、前言

StreamAPI在Java8版本中使用，关注的是对数据的筛选、查找、存储等

它可以做的事情有：过滤、排序、映射、归约

二、使用流程

Stream实例化中间操作（过滤、排序、映射、规约）终止操作（匹配查找、归约、收集）

三、案例演示

 public class EmployeeData { public static List getEmployees(){ List list = new ArrayList<>(); list.add(new Employee(1001, "马化腾", 34, 6000.38)); list.add(new Employee(1002, "马云", 12, 9876.12)); list.add(new Employee(1003, "刘强东", 33, 3000.82)); list.add(new Employee(1004, "雷军", 26, 7657.37)); list.add(new Employee(1005, "李彦宏", 65, 5555.32)); list.add(new Employee(1006, "比尔盖茨", 42, 9500.43)); list.add(new Employee(1007, "任正非", 26, 4333.32)); list.add(new Employee(1008, "扎克伯格", 35, 2500.32)); return list; } }

 package JDK_8; import org.junit.Test; import java.util.Arrays; import java.util.List; import java.util.Optional; import java.util.stream.Collectors; import java.util.stream.Stream; public class StreamAPI { // 方式1：使用集合创建Stream @Test public void test1() { List list = EmployeeData.getEmployees(); // 返回一个顺序流 Stream stream = list.stream(); // 返回一个并行流 Stream employeeStream = list.parallelStream(); } // 方式2：使用数组创建流对象 @Test public void test2() { Employee e1 = new Employee(1003, "WZY", 26, 3000.69); Employee e2 = new Employee(1007, "王紫玉", 25, 8888); Employee[] list2 = new Employee[]{e1, e2}; Stream stream = Arrays.stream(list2); stream.forEach(System.out::println); } // 通过Stream.of 创建 @Test public void test3() { Stream stream = Stream.of(1, 2, 3, 4, 5, 6); stream.forEach(System.out::println); } // Stream.filter进行过滤 @Test public void test4() { List list = EmployeeData.getEmployees(); list.stream().filter(employee -> employee.getAge() > 25).forEach(System.out::println); } // 使用StreamAPI筛选 @Test public void test5() { List list = EmployeeData.getEmployees(); list.add(new Employee(1004, "wzy", 25, 18888)); list.add(new Employee(1004, "wzy", 25, 18888)); list.add(new Employee(1004, "wzy", 25, 18888)); list.add(new Employee(1004, "wzy", 25, 18888)); list.stream().forEach(System.out::println); System.out.println(); list.stream().distinct().forEach(System.out::println); } @Test public void test6() { List list = Arrays.asList("a", "b", "c"); //        map(Function mapper) //        返回由给定函数应用于此流的元素的结果组成的流。 list.stream().map(s -> s.toUpperCase()).forEach(System.out::println); } // 使用StreamAPI筛选：工资大于6000的员工 @Test public void test7() { List list = EmployeeData.getEmployees(); list.stream().filter(s -> s.getSalary() > 6000).forEach(System.out::println); } // StreamAPI映射：map,接收参数，将参数转换为其他形式的信息； @Test public void test8() { List list = EmployeeData.getEmployees(); list.stream().map(e -> e.getAge()).forEach(System.out::println); } // StreamAPI排序,sorted帮助实现Comparable接口进行对象比较 @Test public void test9() { List list = EmployeeData.getEmployees(); list.stream().sorted((e1, e2) -> { int ageValue = Integer.compare(e1.getAge(), e2.getAge()); if (ageValue != 0) { return ageValue; } else { return Double.compare(e1.getSalary(), e2.getSalary()); } }).forEach(System.out::println); } // StreamAPI匹配:所有元素是否满足下列条件 @Test public void test10() { List list = EmployeeData.getEmployees(); boolean allMatch = list.stream().allMatch(e -> e.getSalary() > 5000); System.out.println(allMatch); } // StreamAPI查找：返回第一个元素 @Test public void test11() { List list = EmployeeData.getEmployees(); Optional first = list.stream().findFirst(); System.out.println(first); } // StreamAPI查找：返回薪水数最大的员工 @Test public void test12() { List list = EmployeeData.getEmployees(); Stream salaryStream = list.stream().map(e -> e.getSalary()); Optional max = salaryStream.max(Double::compare); System.out.println(max); } // StreamAPI查找：薪水最小的员工对像 @Test public void test13() { List list = EmployeeData.getEmployees(); Optional min = list.stream().min((e1, e2) -> Double.compare(e1.getSalary(), e2.getSalary())); System.out.println(min); } // StreamAPI:归约 @Test public void test14() { List list = EmployeeData.getEmployees(); Stream salaryStream = list.stream().map(e -> e.getSalary()); Optional sum = salaryStream.reduce((s1, s2) -> s1 + s2); System.out.println(sum.get()); } // StreamAPI：收集 @Test public void test15(){ List list = EmployeeData.getEmployees(); List employeeList = list.stream().filter(e -> e.getSalary() > 5000).collect(Collectors.toList()); for (Employee employee : employeeList) { System.out.println(employee); } } }