stream流，转set和map

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package com.mayikt.stream;   import com.mayikt.entity.UserEntity;   import java.util.ArrayList; import java.util.List; import java.util.Map; import java.util.Optional; import java.util.Set; import java.util.stream.Collectors; import java.util.stream.Stream;   public class Test01 {     public static void main(String[] args) {         List<UserEntity> userEntityList = new ArrayList<>();         userEntityList.add(new UserEntity("mayikt", 20));         userEntityList.add(new UserEntity("meite", 28));         userEntityList.add(new UserEntity("zhangsan", 35));         userEntityList.add(new UserEntity("xiaowei", 16));         userEntityList.add(new UserEntity("xiaowei", 16));           /**          * 创建stream两种方式          * 1.串行流          * 2.并行流          */         Stream<UserEntity> stream = userEntityList.stream();           /**          * 转换成set集合          */         Set<UserEntity> userSet = stream.collect(Collectors.toSet());         userSet.forEach(userEntity -> System.out.println(userEntity));           /**          * stream将list转换成map          * list集合只有元素，此处将user的userName作为key，user对象作为value，转map          */         /*         Map<String, UserEntity> userEntityMap = userSet.stream().collect(Collectors.toMap(new Function<UserEntity, String>() {             @Override             public String apply(UserEntity userEntity) {                 return userEntity.getUserName();             }         }, new Function<UserEntity, UserEntity>() {             @Override             public UserEntity apply(UserEntity userEntity) {                 return userEntity;             }         }));         */         Map<String, UserEntity> userEntityMap = userSet.stream()                 .collect(Collectors.toMap(userEntity -> userEntity.getUserName(), userEntity -> userEntity));         userEntityMap.forEach((k, v) -> System.out.println(k + "," + v));           /**          * Stream reduce求和          */         Stream<Integer> integerStream = Stream.of(10, 50, 30 ,20);         Optional<Integer> reduce = integerStream.reduce((a1, a2) -> a1 + a2);         System.out.println(reduce.get());     } }

　　

注意：stream转set的时候，set是去重的，因此UserEntity要重写equals和hashCode。

UserEntity：

package com.mayikt.entity;

import java.util.Objects;

public class UserEntity {

    private String userName;
    private int age;

    public UserEntity(String userName, int age) {
        this.userName = userName;
        this.age = age;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        UserEntity that = (UserEntity) o;
        return age == that.age &&
                Objects.equals(userName, that.userName);
    }

    @Override
    public int hashCode() {

        return Objects.hash(userName, age);
    }

    @Override
    public String toString() {
        return "UserEntity{" +
                "userName='" + userName + '\'' +
                ", age=" + age +
                '}';
    }
}