java 8 Lambda 表达式用例（Lambda expressions example）

java 8 Lambda 表达式用例

import lombok.AllArgsConstructor;
import lombok.Data;
import org.junit.Test;

import java.util.*;
import java.util.function.Consumer;
import java.util.function.Predicate;

import static java.util.stream.Collectors.joining;
import static java.util.stream.Collectors.toList;
import static java.util.stream.Collectors.toSet;
/**
 * @description: Lambda expressions example
 * @author zivs.zheng
 * @date 2018/3/23 11:27
 */
public class LambdaExample {

    // java 开发人员集合
    List javaPersons = new ArrayList() {{
        add(new Person("Tom", "java development", "M", 2000, 28));
        add(new Person("Bob", "java development", "M", 2500, 22));
        add(new Person("Fei", "java development", "F", 1900, 21));
        add(new Person("Jac", "java development", "M", 2300, 25));
        add(new Person("Hua", "java development", "F", 1800, 22));
        add(new Person("Wei", "java development", "F", 2000, 23));
        add(new Person("Tao", "java development", "M", 3000, 27));
    }};

    // go 开发人员集合
    List goPersons = new ArrayList() {{
        add(new Person("Men", "go development", "F", 2000, 24));
        add(new Person("Mao", "go development", "M", 2500, 23));
        add(new Person("Qin", "go development", "F", 1900, 22));
        add(new Person("Don", "go development", "M", 2300, 25));
        add(new Person("Han", "go development", "M", 2400, 28));
    }};


    @Test
    public void iterateJavaPersons() {
        // Lambda表达式迭代java开发人员集合
        javaPersons.forEach((p) -> System.out.println(p.getName() + "\t" + p.getSalary()));

        System.out.println("增加销售额10%:");
        Consumer giveRaise = e -> e.setSalary(e.getSalary() / 100 * 10 + e.getSalary());
        javaPersons.forEach(giveRaise);
        javaPersons.forEach((p) -> System.out.println(p.getName() + "\t" + p.getSalary()));
    }


    @Test
    public void sortJavaPersons() {

        Collections.sort(javaPersons, new Comparator() {
            @Override
            public int compare(Person p1, Person p2) {
                if (p1.getAge() > p2.getAge()) {
                    return 1;
                }
                return -1;
            }
        });
        javaPersons.forEach((p) -> System.out.println(p.getName() + "\t" + p.getAge()));
        System.out.println();

        // 匿名内部内
        javaPersons.sort((Person p1, Person p2) -> {
            if (p1.getAge() > p2.getAge()) {
                return 1;
            }
            return -1;
        });
        // Lambda表达式迭代java开发人员集合
        javaPersons.forEach((p) -> System.out.println(p.getName() + "\t" + p.getAge()));
    }


    @Test
    public void filterJavaPersons() {
        // 定义 filters
        Predicate ageFilter = (p) -> (p.getAge() > 25);
        Predicate salaryFilter = (p) -> (p.getSalary() > 2000);
        Predicate genderFilter = (p) -> ("M".equals(p.getGender()));

        System.out.println("过滤年龄大于25销售额大于2000性别为M的:");
        javaPersons.stream()
                .filter(ageFilter)
                .filter(salaryFilter)
                .filter(genderFilter)
                .forEach((p) -> System.out.println(p));
        System.out.println();
        System.out.println("过滤年龄大于25销售额大于2000的:");
        goPersons.stream()
                .filter(ageFilter)
                .filter(salaryFilter)
                .forEach((p) -> System.out.println(p));

    }

    @Test
    public void limitPersons() {
        // 根据name排序的前五个
        List result = javaPersons
                .stream()
                .sorted((p1, p2) -> (p1.getName().compareTo(p2.getName())))
                .limit(5)
                .collect(toList());
        result.forEach((p) -> System.out.println(p));
    }

    @Test
    public void minMaxPersons() {
        System.out.println("销售额最小:");
        Person minPerson = javaPersons
                .stream()
                .min((p1, p2) -> (p1.getSalary() - p2.getSalary()))
                .get();
        System.out.println(minPerson);
        System.out.println();
        System.out.println("销售额最大:");
        Person maxPerson = javaPersons
                .stream()
                .max((p1, p2) -> (p1.getSalary() - p2.getSalary()))
                .get();
        System.out.println(maxPerson);
    }

    @Test
    public void sumSalaryPersons() {
        // Salary 之和
        int totalSalary = javaPersons
                .parallelStream()
                .mapToInt(p -> p.getSalary())
                .sum();
        System.out.println(totalSalary);
    }

    @Test
    public void setPersons() {
        // 获取姓名的集合
        Set mapPersons = javaPersons
                .stream()
                .map(Person::getName)
                .collect(toSet());
        mapPersons.forEach(m -> System.out.println(m.toString()));


        System.out.println();
        // 以“,”拼接姓名
        String personsStr = javaPersons
                .stream()
                .map(Person::getName)
                .collect(joining(" , "));
        System.out.println(personsStr);
    }

    @Test
    public void statsPersons() {
        IntSummaryStatistics stats = javaPersons
                .stream()
                .mapToInt((p) -> p.getAge())
                .summaryStatistics();

        System.out.println("Max age : " + stats.getMax());
        System.out.println("Min age : " + stats.getMin());
        System.out.println("Sum age : " + stats.getSum());
        System.out.println("Avg age : " + stats.getAverage());
    }

    @Test
    public void variables() {
        int n = 0;
        final int k = n;
        Runnable r = () -> {
            int i = k;
            System.out.println("i = " + i);
        };
        n++;
        r.run();
    }

}

@Data
@AllArgsConstructor
class Person {
    private String name, job, gender;
    private int salary, age;
}