测试对象

public class Person {private  String  name;private  Integer  age;private  Integer  weight;public Person() {}public Integer getWeight() {return weight;}public void setWeight(Integer weight) {this.weight = weight;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}
}

测试数据

两个list的交集、差集、并集

package Map;import com.alibaba.fastjson.JSON;import java.util.*;
import java.util.stream.Collectors;public class ListStream {public static void main(String[] args) {List<Person> list = new ArrayList<Person>();Person person1 = new Person();person1.setName("张三");person1.setAge(18);person1.setWeight(50);Person person2 = new Person();person2.setName("李四");person2.setAge(26);person2.setWeight(70);Person person3 = new Person();person3.setName("张三");person3.setAge(26);person3.setWeight(60);list.add(person1);list.add(person2);list.add(person3);List<String> list1 = new ArrayList<>();list1.add("1");list1.add("2");list1.add("3");List<String> list2 = new ArrayList<>();list2.add("2");// 交集List<String> intersection = list1.stream().filter(item -> list2.contains(item)).collect(Collectors.toList());System.out.println("交集:"+JSON.toJSONString(intersection));// 差集 (list1 - list2)List<String> reduce1 = list1.stream().filter(item -> !list2.contains(item)).collect(Collectors.toList());System.out.println("差集1:"+JSON.toJSONString(reduce1));// 差集 (list2 - list1)List<String> reduce2 = list2.stream().filter(item -> !list1.contains(item)).collect(Collectors.toList());System.out.println("差集2:"+JSON.toJSONString(reduce2));// 并集List<String> listAll = list1.parallelStream().collect(Collectors.toList());List<String> listAll2 = list2.parallelStream().collect(Collectors.toList());listAll.addAll(listAll2);System.out.println("并集:"+JSON.toJSONString(listAll));// 去重并集List<String> listAllDistinct = listAll.stream().distinct().collect(Collectors.toList());System.out.println("去重并集:"+JSON.toJSONString(listAllDistinct));}}

过滤

 //过滤出符合条件的数据 保留name等于张三
List<Person> temp = list.stream().filter(a -> a.getName().equals("张三")).collect(Collectors.toList());
//过滤出符合条件的数据 过滤name等于张三
List<Person> temp1 = list.stream().filter(a -> !a.getName().equals("张三")).collect(Collectors.toList());

分组

//List 以Name分组 
Map<String, List<Person>> groupBy = list.stream().collect(Collectors.groupingBy(Person::getName));

去重

//去重
List<String> collect = list.stream().map(Person::getName).distinct().collect(Collectors.toList());
//去重 返回list对象
List<Person> unique = list.stream().collect(collectingAndThen(toCollection(() -> new TreeSet<>(comparingLong(Person::getAge))), ArrayList::new));

排序

//排序-->升序
List<Person> sortName = list.stream().sorted(Comparator.comparing(Person::getAge)).collect(Collectors.toList());
String sortName1 = JSON.toJSONString(sortName);
System.out.println("升序:"+sortName1);
//排序-->降序
List<Person> temp2 = list.stream().sorted(Comparator.comparing(Person::getAge).reversed()).collect(Collectors.toList());
String sortName2 = JSON.toJSONString(temp2);
System.out.println("降序:"+sortName2);
//排序-->两个字段排序 如果年龄相同,再使用体重排序
List<Person> temp3 = list.stream().sorted(Comparator.comparing(Person::getAge).thenComparing(Person::getName)).collect(Collectors.toList());
String sortName3 = JSON.toJSONString(temp3);
System.out.println("两个字段排序:"+sortName3);

聚合-->求和,最大值,最小值,平均值,统计

//mapToInt(),mapToDouble(),mapToLong()等
list.stream().mapToDouble(Person::getHeight).sum();//和
list.stream().mapToDouble(Person::getHeight).max();//最大
list.stream().mapToDouble(Person::getHeight).min();//最小
list.stream().mapToDouble(Person::getHeight).average();//平均值
list.stream().mapToDouble(Person::getHeight).count();//统计

list中本身存的就是基本类型的数字

List<Integer> listInteger = Arrays.asList(10,20,30);
listInteger.add(10);
listInteger.add(20);
Integer sum= listInteger.stream().reduce(Integer::sum).orElse(0);
Integer max = listInteger.stream().reduce(Integer::max).orElse(0);

List集合拼接成逗号分隔的字符串

List<String> listStr = Arrays.asList("a", "b", "c");
//String自带方式
String s2 = String.join(",", listStr);
System.out.println(s2);
//用stream流
String s = listStr.stream().collect(Collectors.joining(","));
System.out.println(s);