jdk1.8新特性的应用-Stream 的终止操作

public class TestStreamApi4 {List<Employee> emps = Arrays.asList(new Employee("张三", 23, 14000.11, "深圳"),new Employee("李四", 34, 26000.33, "北京"),new Employee("王五", 55, 18000.00, "上海"),new Employee("赵六", 32, 22000.88, "广州"),new Employee("田七", 23, 14000.11, "深圳"));/** 收集* collect--将流转换为其他形式.接收一个Collector接口得实现,用于给Stream中的元素做汇总的方法* */@Testpublic void test1() {//1.收集所有员工的姓名List<String> list = emps.stream().map(Employee::getName).collect(Collectors.toList());System.out.println("list = " + list);//list = [张三, 李四, 王五, 赵六, 田七]}@Testpublic void test2() {//2.收集所有员工的地址并去重     Employee::getAddress = ->e.getAddress()Set<String> set = emps.stream().map(Employee::getAddress).collect(Collectors.toSet());System.out.println("set = " + set);//set = [上海, 广州, 深圳, 北京]}/** 计算* */@Testpublic void test3() {//总数Long lo = emps.stream().collect(Collectors.counting());System.out.println("lo = " + lo); //lo = 5//平均值Double aDouble = emps.stream().collect(Collectors.averagingDouble(Employee::getSalary));System.out.println("aDouble = " + aDouble); // aDouble = 18800.286//总和Double aDouble1 = emps.stream().collect(Collectors.summingDouble(e -> e.getSalary()));System.out.println("aDouble1 = " + aDouble1);//aDouble1 = 94001.43000000001//最大值Optional<Employee> max = emps.stream().collect(Collectors.maxBy((e1, e2) -> Double.compare(e1.getSalary(), e2.getSalary())));System.out.println(max.get());//Employee{name='李四', age=34, salary=26000.33, address='北京'}//最小值Optional<Employee> min = emps.stream().collect(Collectors.minBy((e1, e2) -> Double.compare(e1.getSalary(), e2.getSalary())));System.out.println(min.get());//Employee{name='张三', age=23, salary=14000.11, address='深圳'}}/** 分组* */@Testpublic void test4() {//按照地址分组Map<String,List<Employee>> map = emps.stream().collect(Collectors.groupingBy(Employee::getAddress));System.out.println("map = " + map);//map = {广州=[Employee{name='赵六', age=32, salary=22000.88, address='广州'}], 上海=[Employee{name='王五', age=55,// salary=18000.0, address='上海'}], 北京=[Employee{name='李四', age=34, salary=26000.33, address='北京'}],// 深圳=[Employee{name='张三', age=23, salary=14000.11, address='深圳'}, Employee{name='田七', age=23,// salary=14000.11, address='深圳'}]}}/** 分区* */@Testpublic void test5() {Map<Boolean, List<Employee>> map = emps.stream().collect(Collectors.partitioningBy(e -> e.getSalary()>15000));System.out.println("map = " + map);//map = {false=[Employee{name='张三', age=23, salary=14000.11, address='深圳'}, Employee{name='田七', age=23, salary=14000.11, address='深圳'}], true=[Employee{name='李四', age=34, salary=26000.33, address='北京'}, Employee{name='王五', age=55, salary=18000.0, address='上海'}, Employee{name='赵六', age=32, salary=22000.88, address='广州'}]}}
}

练习

package com.gl.testLambda;import org.junit.Test;import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.Set;
import java.util.stream.Collectors;/*** Created by IntelliJ Idea 2018.1* Author:Gavin Zhang* Data:  2021-08-03* Time:  21:42*/
public class TestStreamApi5 {List<TradeList> tradeLists = Arrays.asList(new TradeList("唐僧","东土大唐","2008",2000),new TradeList("孙悟空","花果山","2008",1500),new TradeList("猪八戒","高老庄","2008",1000),new TradeList("沙和尚","流沙河","2008",800),new TradeList("刘备","蜀","2009",3000),new TradeList("关羽","蜀","2009",2200),new TradeList("张飞","蜀","2009",2000),new TradeList("曹操","魏","2010",1500),new TradeList("曹丕","魏","2010",1500));/** 练习* */@Testpublic void test1() {//1.找出2008年发生的所有交易订单,并按照交易额从小到大排序List<TradeList> collect = tradeLists.stream().filter(e -> e.getYear().equals("2008")).sorted((e1,e2)->Double.compare(e1.getTradeAmount(),e2.getTradeAmount())).collect(Collectors.toList());System.out.println("collect = " + collect);//collect = [TradeList{name='沙和尚', city='流沙河', year='2008', tradeAmount=800.0}, TradeList{name='猪八戒',// city='高老庄', year='2008', tradeAmount=1000.0}, TradeList{name='孙悟空', city='花果山', year='2008',// tradeAmount=1500.0}, TradeList{name='唐僧', city='东土大唐', year='2008', tradeAmount=2000.0}]}@Testpublic void test2() {//2.交易员都在哪些不同的城市List<String> collect = tradeLists.stream().map(e -> e.getCity()).distinct().collect(Collectors.toList());System.out.println("collect = " + collect);//collect 有序 = [东土大唐, 花果山, 高老庄, 流沙河, 蜀, 魏]Set<String> collect1 = tradeLists.stream().map(e -> e.getCity()).collect(Collectors.toSet());System.out.println("collect1 = " + collect1);//collect1 无序 = [蜀, 花果山, 流沙河, 高老庄, 东土大唐, 魏]}@Testpublic void test3() {//3.查找出来自蜀的交易员,并按照姓名排序List<String> list = tradeLists.stream().filter(t -> t.getCity().equals("蜀")).collect(Collectors.toList()).stream().map(e -> e.getName()).sorted().collect(Collectors.toList());System.out.println("list = " + list);//list = [关羽, 刘备, 张飞]}@Testpublic void test4() {//4.有没有交易员是在魏工作的boolean anyMatch = tradeLists.stream().anyMatch(e -> e.getCity().equals("蜀"));System.out.println("anyMatch = " + anyMatch);}@Testpublic void test5() {//5.计算生活在蜀的交易员的所有交易额Optional<Double> sum = tradeLists.stream().filter(e -> e.getCity().equals("蜀")).map(e->e.getTradeAmount()).reduce(Double::sum);System.out.println(sum.get());//7200.0Optional<Double> sum2 = tradeLists.stream().filter(e -> e.getCity().equals("蜀")).collect(Collectors.toList()).stream().map(e -> e.getTradeAmount()).reduce(Double::sum);System.out.println(sum2.get());//7200.0}@Testpublic void test6() {//6.所有交易中,最少/最高的交易额是多少//最少Optional<Double> min = tradeLists.stream().map(e -> e.getTradeAmount()).sorted().collect(Collectors.toList()).stream().findFirst();System.out.println(min.get());//800.0//最少Optional<Double> min1 = tradeLists.stream().map(e -> e.getTradeAmount()).min(Double::compareTo);System.out.println(min1.get());//800.0//最多Optional<Double> max = tradeLists.stream().map(e -> e.getTradeAmount()).max(Double::compareTo);System.out.println(max.get());//3000.0}@Testpublic void test7() {//找到交易额最小的交易信息Optional<TradeList> min = tradeLists.stream().min((e1, e2) -> Double.compare(e1.getTradeAmount(), e2.getTradeAmount()));System.out.println(min.get());//TradeList{name='沙和尚', city='流沙河', year='2008', tradeAmount=800.0}Optional<TradeList> max = tradeLists.stream().max((e1, e2) -> Double.compare(e1.getTradeAmount(), e2.getTradeAmount()));System.out.println(max.get());//TradeList{name='刘备', city='蜀', year='2009', tradeAmount=3000.0}}
}

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