0806strem流试炼2--持续更新

关注公众号：”奇叔码技术“
回复： “java面试题大全”或者“java面试题”
即可免费领取资料


携手创作，共同成长！这是我参与「掘金日新计划 · 8 月更文挑战」的第5天，点击查看活动详情

package util;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.extern.log4j.Log4j2;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.*;
import java.util.function.Function;
import java.util.stream.Collectors;


 //strem流试炼2
@SpringBootTest
public class StreamTest {

    private  Logger logger  = LoggerFactory.getLogger(this.getClass());

    //一个接口中存放多个对象--一般用于一个entity实体类以外所有关的vo（值对象）、dto（数据传输对象）等对象都可以存放在一起（类少些了，也方便查询和删改）
    public interface  CollectionData{

        @Data
        @NoArgsConstructor
        @AllArgsConstructor
        public class A{
            private Long id;
            private String name;
            private Long age;
            private String sex;

            public A(String name, Long age, String sex) {
                this.name = name;
                this.age = age;
                this.sex = sex;
            }
        }


        @Data
        @NoArgsConstructor
        @AllArgsConstructor
        public class ADTO{
            private Long age;
            private String sex;
        }

    }
   


    //stream().distinct() 一般用于对象的完全去重
    @Test
    public void streamDistinct(){
        ArrayList<CollectionData.A> aLists = new ArrayList<>();
        CollectionData.A a1 = new CollectionData.A("小明", 1l, "男");
        CollectionData.A a2 = new CollectionData.A("小明2", 2l, "男2");
        CollectionData.A a3 = new CollectionData.A("小明3", 3l, "男3");
        CollectionData.A a4 = new CollectionData.A("小明3", 3l, "男3");
        aLists.add(a1);
        aLists.add(a2);
        aLists.add(a3);
        aLists.add(a4);

        //1、进行去重，只有两个完全一样的对象才会去重，这里去重了最后一个对象

        List<CollectionData.A> collect = aLists.stream().distinct().collect(Collectors.toList());
        //[StreamTest.CollectionData.A(id=null, name=小明, age=1, sex=男),
        // StreamTest.CollectionData.A(id=null, name=小明2, age=2, sex=男2),
        // StreamTest.CollectionData.A(id=null, name=小明3, age=3, sex=男3)]

        logger.info("{}",collect);
    }


    //stream().distinct() 一般用于某个字段的去重
    @Test
    public void streamDistinctFields(){
        ArrayList<CollectionData.A> aLists = new ArrayList<>();
        CollectionData.A a1 = new CollectionData.A("小明", 1l, "男");
        CollectionData.A a2 = new CollectionData.A("小明3", 2l, "男2");
        CollectionData.A a3 = new CollectionData.A("小明3", 3l, "男3");
        CollectionData.A a4 = new CollectionData.A("小明3", 3l, "男3");
        aLists.add(a1);
        aLists.add(a2);
        aLists.add(a3);
        aLists.add(a4);

        //1、进行去重，比对，某个字段进行去重，一般用于sql查询之后的结果（或者sql进行group by分组），再做某个字段的去重
        //这里进行去重，name相同的进行去重
        ArrayList<CollectionData.A> collect = aLists.stream().collect(
                Collectors.collectingAndThen(Collectors.toCollection(
                        () -> new TreeSet<>(Comparator.comparing(new Function<CollectionData.A, String>() {
                            @Override
                            public String apply(CollectionData.A a) {
                                return a.getName();
                            }
                        }))), ArrayList::new));

        logger.info("{}",collect);
        //[StreamTest.CollectionData.A(id=null, name=小明, age=1, sex=男),
        // StreamTest.CollectionData.A(id=null, name=小明3, age=2, sex=男2)]
    }

   

}