java Collection.stream操作

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class Test2
{

    public static void main(String[] args) {
    	List<Stu> list=new ArrayList();
    	Stu stu1=new Stu(15, "张飞");
    	Stu stu2=new Stu(19, "关于");
    	Stu stu3=new Stu(22,"刘备");
    	list.add(stu1);
    	list.add(stu2);
    	list.add(stu3);
    	Collections.shuffle(list);
    	/* 操作步骤：集合->生成流->中间操作->终端操作
    	 * eg: list.stream.limit(2).collect(Collectors.toList());
    	 * 
    	 *
    	 * 1.中间操作
    	 * - 操作流
    	 * map
    	 * filter
    	 * limit
    	 * sort
    	 * reduce
    	 * max min count distinct
    	 * foreach
    	 * match
    	 * 
    	 * 2.终端操作
    	 *-对操作后的流进行组织后返回。
    	 *     .collect( Collectors.doSomeThing);
    	 * summarizing：getMax ,min count sum avarage
    	 * grouping by
    	 * joining
    	 * partitioningBy
    	 * 
    	 * 
    	 */
//对流的操作 ：过滤，映射，排序，
    	Map<String,String> map=new HashMap<>();
    	System.out.println("=========list===========");
    	System.out.println(list);
    	System.out.println("=====filter(Predicate):过滤集合 ==========");
    	List<Stu> filterList=list.stream().filter(u->u.age>=19&&"关于".equals(u.name)).collect(Collectors.toList());
    	System.out.println("======map(Function)  根据输入(类型A)获取输出(类型B)  ==========");
    	List<Stu> mapList=list.stream().map(a->new Stu(a.age+2, a.name)).collect(Collectors.toList());
    	List<Integer> mapList2=list.stream().map(a->a.age+2).collect(Collectors.toList());
    	System.out.println(mapList);
    	System.out.println("========limit ========");
    	List<Stu> limitList=list.stream().limit(2).collect(Collectors.toList());
    	System.out.println(limitList);
    	System.out.println("========sorted  排序========");
    	List<Stu> sortList = list.stream().sorted(Comparator.comparing(a->a.age)).collect(Collectors.toList());
    	List<Stu> reverseSortList = list.stream().sorted(Comparator.comparing(a->a.age, Comparator.reverseOrder())).collect(Collectors.toList());
    	System.out.println(reverseSortList);
    	System.out.println("===reduce  迭代进行归并 ============");
    	int value = Stream.of(1, 2, 3, 4, 5)
    			.reduce(((item1, item2) -> item1 + item2)).get();
    	
    	
    	System.out.println("===============foreach  遍历Consumer==========");
    	list.stream().forEach(a->a.age=a.age+3);    	
    	System.out.println(list);
    	System.out.println("=========================match匹配=========");
    	System.out.println(list.stream().anyMatch(a->a.age<12));
//=======================================================Collectors===================================================================================
    	System.out.println("========average  平均数=======");
    	System.out.println(""+list.stream().collect(Collectors.averagingInt(a->a.age)));
    	System.out.println("=========group by  分组======");
    	Map<Object, List<Stu>>groupMap=list.stream().collect(Collectors.groupingBy(a->a.age));
    	System.out.println(groupMap);

    	System.out.println("====group by counting  分组统计==========");
    	Map<Object, Long>groupCountMap=list.stream().collect(Collectors.groupingBy(a->a.age,Collectors.counting()));
    	System.out.println(groupCountMap);
    	System.out.println("==============summarizing  统计===");
    	System.out.println(list.stream().collect(Collectors.summarizingInt(a->a.age)).getMax());
    	System.out.println("=========mapping  T->R =====");
		List<Stu> mapping=list.stream().collect(Collectors.mapping(a->new Stu(a.age+2, a.name),Collectors.toList() ));

    	
//避免空指针异常 Potional.ofNullable().map()....orElse();
    	String s=Optional.ofNullable(new Stu(12,"22")).map(Stu::getName).orElse(null);
    

		
    	
    }

}

class Stu{
	int age;
	String name;
	public Stu(int age, String name) {
		super();
		this.age = age;
		this.name = name;
	}
	public String getName() {
		return name;
	}
	@Override
	public String toString() {
		return "Stu [age=" + age + ", name=" + name + "]";
	}
	
}