java8 函数式编程

	/***
	 * 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;
	}

}