说明:这是基于同事(cal,多谢)的培训材料做的练习，记录下来，以作日后自己coding分析和改进
1.准备
Dish.java
package com.example.demo; import lombok.AllArgsConstructor; import lombok.Data; /** * Created by Administrator on 2019/9/7. */ @Data @AllArgsConstructor public class Dish { private int calories; private String name; }
List<Dish> list;
list = Lists.newArrayList(
new Dish( 1,"aa"),
new Dish(13,"bb"),
new Dish(7,"cc"),
new Dish( 6,"aa"),
new Dish(9,"dd"),
new Dish(1,"ee"),
new Dish( 3,"aa"),
new Dish(1,"ff"),
new Dish(1,"gg")
);
2.stream的创建
Integer[] ints={1,2};
List<Integer> list2=Lists.newArrayList(ints);
List<String> collect3 = list2.stream().map(o -> "1" + o).collect(Collectors.toList());
List<String> collect4 = Stream.of(1,2).map(o -> "1" + o).collect(Collectors.toList());
List<String> collect5 = Stream.of(ints).map(o -> "1" + o).collect(Collectors.toList());
List<String> collect6 = Stream.of(list2).map(o -> "1" + o).collect(Collectors.toList());
System.out.println(collect3);
System.out.println(collect4);
System.out.println(collect5);
System.out.println(collect6);
输出：
[11, 12]
[11, 12]
[11, 12]
[1[1, 2]]
3.list转map并排序
list排序参照java8排序 java8 list转Map报错Collectors.toMap :: results in "Non-static method cannot be refernced from static context"
TreeMap<String, String> collect1 = list.stream() .collect(Collectors.toMap(Dish::getName, o -> "", (key1, key2) -> key2, TreeMap<String, String>::new));
System.out.println(collect1);
输出：{aa=, bb=, cc=, dd=, ee=, ff=, gg=}
4.list转linkedList
LinkedList<Dish> collect2 = list.stream().collect(Collectors.toCollection(LinkedList::new));
输出：[Dish(calories=1, name=aa), Dish(calories=13, name=bb), Dish(calories=7, name=cc), Dish(calories=6, name=aa), Dish(calories=9, name=dd), Dish(calories=1, name=ee), Dish(calories=3, name=aa), Dish(calories=1, name=ff), Dish(calories=1, name=gg)]
5.filter，map，sorted,limit,collect的使用
List<String> collect = list.stream() .filter(d ->d.getCalories() < 9) .sorted(Comparator.comparing(Dish::getCalories).reversed()) .map(d->d.getName()) .limit(3)
输出：[cc, aa, aa]
打印日志：
List<String> collect = list.stream() .filter(d ->{ System.out.println("filter "+d.getName()); return d.getCalories() < 9;}) .sorted(Comparator.comparing(Dish::getCalories).reversed()) .map(d->{ System.out.println("map "+d.getName()); return d.getName(); }) .limit(3) .collect(Collectors.toList());
System.out.println(collect);
输出：
filter aa
filter bb
filter cc
filter aa
filter dd
filter ee
filter aa
filter ff
filter gg
map cc
map aa
map aa
[cc, aa, aa]
原文：https://www.cnblogs.com/pu20065226/p/11483698.html