/***

	 * 测试统计API <br>

	 * 小结:<br>

	 * 1.逻辑代码应用{} 包起来  不写{} 默认  + return <br>

	 * 2.重载方法参数必须加类型声明<br>

	 * 3.书写风格一个表达式只做一次抽象转换 <br>

	 * 4.最后断链了 stream 内部会关闭流,再执行流之类操作会抛异常<br>

	 * 5.表达式可以象管道一样绑定,接口与另一实例方法绑定<br>

	 * */

	public static class Test4 {

		public static void main(String[] args) {

			List<Person> list1 = Person.ofList();

 			//sum 操作

			long count = list1.stream().mapToInt(e -> e.getAge()).sum();

			//reduce 操作

			long count2 = list1.stream().mapToInt(e -> e.getAge()).reduce(0, (a,b)->a+b);

			//max 操作

			OptionalInt max = list1.stream().mapToInt(e -> e.getAge()).max();

			//avg 操作

			OptionalDouble count1 = list1.stream().mapToInt(e -> e.getAge()).average();

			//返回统计对象

			IntSummaryStatistics statistics=list1.stream().mapToInt(e -> e.getAge()).summaryStatistics();

			//groupBy 操作

			Map<Integer, List<Person>> map=list1.stream().collect(Collectors.groupingBy(Person::getAge));

			//collect 集合结束操作

			Collectors.toList();

			Collectors.toSet();

			//每次it 回调peek

			list1.stream().filter(e->e.getAge()>2).mapToInt(e -> e.getAge()).peek( e->System.out.println("peek : "+e)).count();

			//接口与实例方法绑定

			list1.stream().forEach(System.out::println);

			//并行流

			list1.parallelStream().count();

			System.out.println("count : " + count);

			System.out.println("count2 : " + count2);

			System.out.println("aver : " + count1.getAsDouble());

			System.out.println("max : " + max.getAsInt());

			System.out.println("statistics count : " + statistics.getCount());

			System.out.println("groupBy size : " + map.size());

			Map<String,String> m = new HashMap<>();

			m.getOrDefault("a", "5");

			m.merge("a", "addValue", (a,b)-> a+b);

			System.out.println("map merge : " + m.get("a"));

		}

	}

import java.util.ArrayList;

import java.util.List;

public class Person {

	private String name;

	private int age;

	public static Person of(String name, int age) {

		Person result = new Person();

		result.name = name;

		result.age = age;

		return result;

	}

	public Person() {

	}

	public Person(String name, int age) {

		this.name = name;

		this.age = age;

	}

	public static List<Person> ofList() {

		List<Person> result = new ArrayList<>();

		for (int i = 0; i < 50; i++) {

			result.add(of("a" + i, i % 5));

		}

		return result;

	}

	public String getName() {

		return name;

	}

	public int getAge() {

		return age;

	}

}