java8 lambda表达式和stream流学习笔记

供自己以后查阅

https://cloud.tencent.com/developer/article/1187833

https://blog.csdn.net/yinhaoh/article/details/104674883/

https://www.jianshu.com/p/9f34edcbe817

 

java8中Collectors的方法使用实例

https://blog.csdn.net/u014231523/article/details/102535902

不错的博

 例子 user类

	// stream().forEach()遍历集合
	list.stream().forEach(user->{System.out.println(user.getId());});

	//分组
	// Collectors.groupingBy(User::getSex)其实是Collectors.groupingBy(User::getSex,Collectors.toList())的缩写，还可以计算count求和等
	Map> groupByCity = userList.stream().collect(Collectors.groupingBy(User::getSex));
	
	//遍历分组
	for (Map.Entry> entryUser : groupBySex.entrySet()) {
    	String key = entryUser.getKey();
    	List entryUserList = entryUser.getValue();
	}

	// 多分组字段
	// 字段写入
	Function> compositeKey = f -> Arrays.