2java后端 3基本 2Collectioin - 菜鸟乙

1　　　　集合List

1.1　　　　遍历

遍历 List链表

　　　for (int i = 0; i < list.size(); i++) {
            News s = (News)list.get(i);
            System.out.println(s.getId()+"  "+s.getTitle()+"  "+s.getAuthor());
　　　　}

　　　　for (News s : list) {
            System.out.println(s.getId()+"  "+s.getTitle()+"  "+s.getAuthor());
　　　}

    public static void main(String[] args) {

        List<Person> personList = Arrays.asList(new Person("17","小美"),new Person("18","小明"));
        Iterator<Person> it = personList.listIterator();
        while(it.hasNext()){
            Person person = (Person) it.next();
            System.out.println(person);
        }
    }

遍历 Map映射

for(int key: hashMap3.keySet()){
         priorityQueue.enqueue(new MapInnerClass(key,hashMap3.get(key)));
}

1.2　　　　三种调用形式的使用场景

如果需要操作索引，使用普通for循环。
如果在遍历的过程中需要删除元素，请使用迭代器。
如果仅仅想遍历，那么使用增强for。

1.3　　　　jdk8新特性

map的使用（参见5.1）
foreach的使用（参见5.1）
map与foreach的区别
groupingBy方法（参见6.4）
reducing应用把流组成新的集合（参见6.5）
collectingAndThen (参见6.5)
list和map互转（参见6.5）

(1)map()会分配内存空间存储新数组并返回，forEach()不会返回数据。

map遍历的后的数组通常都是生成一个新的数组，新的数组的值发生变化，当前遍历的数组值不会变化。

(2)forEach()允许callback更改原始数组的元素。map()返回新的数组。

forEach遍历通常都是直接引入当前遍历数组的内存地址，生成的数组的值发生变化，当前遍历的数组对应的值也会发生变化。

1.4　　　　其他方法

Array.asList demo，参见5.1(不能和list.addAll一起使用)
listA.addAll(listB) 两个list合并成1个list

List<String> newList = Optional.ofNullable(list).map(e->{return e.stream().map(...).collect(Collectors.toList())}).orElse(Lists.newArrayList());   判断非空

List取前n条数据list.subList(0, n);(前包后不包)

1.5　　　　结束for循环，continu,break，return的区别

https://www.cnblogs.com/1446358788-qq/p/16736785.html

2　　　　集合Map

2.1　　　　map之put方法1

package itcast.java16;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;

public class MapDemo1 {

    public static void main(String[] args) {
        Map<String, String> map = new HashMap<String, String>();
        // 添加元素，如果出现添加时,相同的键。那么后添加的值会覆盖原有键对应值。并put方法会返回被覆盖的值。
        map.put("01", "zhangsan1");
        map.put("02", "zhangsan2");
        map.put("03", "zhangsan3");
        System.out.println("get:" + map.get("03"));
        // 可以通过get方法的返回值来判断一个键是否存在。通过返回null来判断
        // 获取map集合中的所有的值
        Collection<String> coll = map.values();
        System.out.println(coll);
        System.out.println(map);
    }
}

2.2　　　　map之put方法2

package com.axjy.aa;

import java.util.*;

public class Test {
public static void main(String[] args) {
Map map=new HashMap();
String s="key";
map.put(s, "hello");
map.put(s, "Wrold");
map.put(s, "value");
System.out.println(map);
}

}

打印的结果是：

{key=value}
"Administrator" Sid: S-1-5-21-1754733684-1616197072-4204698062-500

请格外注意：调试的时候发现变量s的值一直未有改变，而最后的显示结果证明：s已经发生了改变

2.3　　　　map中的entry

是java中的一个对象，一般可以通过map.entrySet()得到。
1，entrySet实现了Set接口，里面存放的是键值对。一个K对应一个V。
2，用来遍历map的一种方法。
Set<Map.Entry<String, String>> entryseSet=map.entrySet();
for (Map.Entry<String, String> entry:entryseSet) {
System.out.println(entry.getKey()+","+entry.getValue());
}
通过getKey（）得到K，getValue得到V。

3　　　　集合Set

4　　　　数组

5　　　　递归

5.1　　　　递归List

背景：

需要从外围系统拿到一个树，转成我们系统的树，但是部分字段不一样(demo中的字段为fatherId到parentId),转的时候发现只转了第一层级，内部层级的没有转化，所以在付哥的帮助下做了递归转换。但是在写博客的时候发现mapStruct是可以进行多层级转换的，经排查也不是版本的问题，反正遇到只转一个层级的情况是可以用递归转换的，这个也作为一个新知识点记录下。

技术栈：

jdk8 lambda表达式：forEach，map使用

mapStruct

递归

json

递归类：

package com.ddwei.test.service;

import com.alibaba.fastjson.JSON;
import com.ddwei.test.dto.recursion.FamilyMember;
import com.ddwei.test.dto.recursion.OutDto;
import lombok.extern.slf4j.Slf4j;
import org.springframework.util.CollectionUtils;

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

@Slf4j
public class DiGui2 {
    private static List<FamilyMember> list;

    private static void  init(){
        FamilyMember familyMember211 = new FamilyMember("211","21","堂妹", new ArrayList<>());
        FamilyMember familyMember21 = new FamilyMember("21","2","堂叔", Arrays.asList(familyMember211));
        FamilyMember familyMember2 = new FamilyMember("2","","二爷",Arrays.asList(familyMember21));

        FamilyMember familyMember111 = new FamilyMember("111","11","姐姐", new ArrayList<>());
        FamilyMember familyMember112 = new FamilyMember("112","11","哥哥", new ArrayList<>());
        FamilyMember familyMember11 = new FamilyMember("11","1","爸爸", Arrays.asList(familyMember111,familyMember112));
        FamilyMember familyMember12 = new FamilyMember("12","1","姑姑", new ArrayList<>());

        FamilyMember familyMember1 = new FamilyMember("1","","爷爷",Arrays.asList(familyMember11,familyMember12));
        list = Arrays.asList(familyMember1,familyMember2);

        //return list;

    }

    /**
     * 递归调用
     * @author weidoudou
     * @date 2022/8/2 12:50
     * @param args 请添加参数描述
     * @return void
     **/
    public static void main(String[] args) {
        init();
        //1     最初的对象list
        log.info("DiGui->main->list->:{}",JSON.toJSONString(list));

        //2     过滤出有最外层对象list,否则
        List<FamilyMember> remotList = list.stream().filter(e->"".equals(e.getFatherId())).collect(Collectors.toList());
        log.info("DiGui->main->remotList->:{}",JSON.toJSONString(remotList));

        //3     最外层的转化
        List<OutDto> outDtoList = remotList.stream().map(DdWeiAssembler.INSTANCE::copyRemotDtoFamilyMemberToDto).collect(Collectors.toList());
        log.info("DiGui->main->outDtoList1->:{}",JSON.toJSONString(outDtoList));

        //4     调用递归方法
        makeTree(outDtoList,remotList);
        log.info("DiGui->main->outDtoList2->:{}",JSON.toJSONString(outDtoList));

    }

    private static void makeTree(List<OutDto> outDtoList,List<FamilyMember> remotList){
        //如果递归传过来的remotList为空（通常children为空）,直接进行下一个循环
        if(CollectionUtils.isEmpty(remotList)){
            return;
        }

        //给新的list赋值
        outDtoList.forEach(outRoot->{
            Iterator<FamilyMember> remotIt = remotList.iterator();
            while(remotIt.hasNext()){
                FamilyMember remotDto = remotIt.next();
                if(outRoot.getId().equals(remotDto.getId())){

                    //如果remotList children返回为null,给空list，否则将children转成新的list
                    outRoot.setChildren(Optional.ofNullable(remotDto.getChildren()).map(e->{
                        return e.stream().map(DdWeiAssembler.INSTANCE::copyRemotDtoFamilyMemberToDto).collect(Collectors.toList());
                    }).orElse(Collections.EMPTY_LIST));

                    //下一层级的递归调用
                    makeTree(outRoot.getChildren(),remotDto.getChildren());
                }
            }
        });
    }


}

remotDto

package com.ddwei.test.dto.recursion;

import lombok.*;

import java.util.List;

@Getter
@Setter
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class FamilyMember {

    private String id;
    private String fatherId;
    private String call;

    private List<FamilyMember> children;

}

outDto

package com.ddwei.test.dto.recursion;

import lombok.*;

import java.util.List;

@Getter
@Setter
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class OutDto {

    private String id;
    private String parentId;
    private String call;

    private List<OutDto> children;

    @Override
    public String toString() {
        return "OutDto{" +
                "id='" + id + '\'' +
                ", fatherId='" + parentId + '\'' +
                ", call='" + call + '\'' +
                ", children=" + children +
                '}';
    }
}

Assembler类：

package com.ddwei.test.service;


import com.ddwei.test.dto.recursion.FamilyMember;
import com.ddwei.test.dto.recursion.OutDto;
import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
import org.mapstruct.Mappings;
import org.mapstruct.factory.Mappers;

@Mapper(componentModel = "spring")
public interface DdWeiAssembler {
    DdWeiAssembler INSTANCE = Mappers.getMapper(DdWeiAssembler.class);

    @Mappings({
            @Mapping(source = "fatherId",target = "parentId")
    })
    OutDto copyRemotDtoFamilyMemberToDto(FamilyMember query);

}

打印日志：

D:\java\envir\jdk1.8\anZh\bin\java.exe "-javaagent:D:\java\develop\idea\anZh\IntelliJ IDEA Community Edition 2021.2.1\lib\idea_rt.jar=61068:D:\java\develop\idea\anZh\IntelliJ IDEA Community Edition 2021.2.1\bin" -Dfile.encoding=UTF-8 -classpath D:\java\envir\jdk1.8\anZh\jre\lib\charsets.jar;D:\java\envir\jdk1.8\anZh\jre\lib\deploy.jar;D:\java\envir\jdk1.8\anZh\jre\lib\ext\access-bridge-64.jar;D:\java\envir\jdk1.8\anZh\jre\lib\ext\cldrdata.jar;D:\java\envir\jdk1.8\anZh\jre\lib\ext\dnsns.jar;D:\java\envir\jdk1.8\anZh\jre\lib\ext\jaccess.jar;D:\java\envir\jdk1.8\anZh\jre\lib\ext\jfxrt.jar;D:\java\envir\jdk1.8\anZh\jre\lib\ext\localedata.jar;D:\java\envir\jdk1.8\anZh\jre\lib\ext\nashorn.jar;D:\java\envir\jdk1.8\anZh\jre\lib\ext\sunec.jar;D:\java\envir\jdk1.8\anZh\jre\lib\ext\sunjce_provider.jar;D:\java\envir\jdk1.8\anZh\jre\lib\ext\sunmscapi.jar;D:\java\envir\jdk1.8\anZh\jre\lib\ext\sunpkcs11.jar;D:\java\envir\jdk1.8\anZh\jre\lib\ext\zipfs.jar;D:\java\envir\jdk1.8\anZh\jre\lib\javaws.jar;D:\java\envir\jdk1.8\anZh\jre\lib\jce.jar;D:\java\envir\jdk1.8\anZh\jre\lib\jfr.jar;D:\java\envir\jdk1.8\anZh\jre\lib\jfxswt.jar;D:\java\envir\jdk1.8\anZh\jre\lib\jsse.jar;D:\java\envir\jdk1.8\anZh\jre\lib\management-agent.jar;D:\java\envir\jdk1.8\anZh\jre\lib\plugin.jar;D:\java\envir\jdk1.8\anZh\jre\lib\resources.jar;D:\java\envir\jdk1.8\anZh\jre\lib\rt.jar;C:\Users\18612\IdeaProjects\text\target\classes;D:\java\maven\apache-maven-3.8.2\repository\org\projectlombok\lombok\1.18.2\lombok-1.18.2.jar;D:\java\maven\apache-maven-3.8.2\repository\org\slf4j\slf4j-api\1.7.30\slf4j-api-1.7.30.jar;D:\java\maven\apache-maven-3.8.2\repository\org\slf4j\slf4j-log4j12\1.7.30\slf4j-log4j12-1.7.30.jar;D:\java\maven\apache-maven-3.8.2\repository\log4j\log4j\1.2.17\log4j-1.2.17.jar;D:\java\maven\apache-maven-3.8.2\repository\org\mapstruct\mapstruct\1.4.2.Final\mapstruct-1.4.2.Final.jar;D:\java\maven\apache-maven-3.8.2\repository\org\mapstruct\mapstruct-jdk8\1.4.2.Final\mapstruct-jdk8-1.4.2.Final.jar;D:\java\maven\apache-maven-3.8.2\repository\org\mapstruct\mapstruct-processor\1.4.2.Final\mapstruct-processor-1.4.2.Final.jar;D:\java\maven\apache-maven-3.8.2\repository\org\mockito\mockito-core\2.23.4\mockito-core-2.23.4.jar;D:\java\maven\apache-maven-3.8.2\repository\net\bytebuddy\byte-buddy\1.9.3\byte-buddy-1.9.3.jar;D:\java\maven\apache-maven-3.8.2\repository\net\bytebuddy\byte-buddy-agent\1.9.3\byte-buddy-agent-1.9.3.jar;D:\java\maven\apache-maven-3.8.2\repository\org\objenesis\objenesis\2.6\objenesis-2.6.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apiguardian\apiguardian-api\1.1.0\apiguardian-api-1.1.0.jar;D:\java\maven\apache-maven-3.8.2\repository\org\opentest4j\opentest4j\1.2.0\opentest4j-1.2.0.jar;D:\java\maven\apache-maven-3.8.2\repository\org\junit\platform\junit-platform-commons\1.5.0\junit-platform-commons-1.5.0.jar;D:\java\maven\apache-maven-3.8.2\repository\org\jmockit\jmockit\1.36\jmockit-1.36.jar;D:\java\maven\apache-maven-3.8.2\repository\junit\junit\4.12\junit-4.12.jar;D:\java\maven\apache-maven-3.8.2\repository\org\hamcrest\hamcrest-core\1.3\hamcrest-core-1.3.jar;D:\java\maven\apache-maven-3.8.2\repository\org\junit\platform\junit-platform-runner\1.6.2\junit-platform-runner-1.6.2.jar;D:\java\maven\apache-maven-3.8.2\repository\org\junit\platform\junit-platform-launcher\1.6.2\junit-platform-launcher-1.6.2.jar;D:\java\maven\apache-maven-3.8.2\repository\org\junit\platform\junit-platform-engine\1.6.2\junit-platform-engine-1.6.2.jar;D:\java\maven\apache-maven-3.8.2\repository\org\junit\platform\junit-platform-suite-api\1.6.2\junit-platform-suite-api-1.6.2.jar;D:\java\maven\apache-maven-3.8.2\repository\com\github\houbb\bean-mapping-core\0.2.5\bean-mapping-core-0.2.5.jar;D:\java\maven\apache-maven-3.8.2\repository\com\github\houbb\bean-mapping-api\0.2.5\bean-mapping-api-0.2.5.jar;D:\java\maven\apache-maven-3.8.2\repository\com\github\houbb\heaven\0.1.62\heaven-0.1.62.jar;D:\java\maven\apache-maven-3.8.2\repository\com\alibaba\fastjson\1.2.47\fastjson-1.2.47.jar;D:\java\maven\apache-maven-3.8.2\repository\org\springframework\spring-context\5.3.18\spring-context-5.3.18.jar;D:\java\maven\apache-maven-3.8.2\repository\org\springframework\spring-aop\5.3.18\spring-aop-5.3.18.jar;D:\java\maven\apache-maven-3.8.2\repository\org\springframework\spring-beans\5.3.18\spring-beans-5.3.18.jar;D:\java\maven\apache-maven-3.8.2\repository\org\springframework\spring-core\5.3.18\spring-core-5.3.18.jar;D:\java\maven\apache-maven-3.8.2\repository\org\springframework\spring-jcl\5.3.18\spring-jcl-5.3.18.jar;D:\java\maven\apache-maven-3.8.2\repository\org\springframework\spring-expression\5.3.18\spring-expression-5.3.18.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\plugins\maven-resources-plugin\2.6\maven-resources-plugin-2.6.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\maven-plugin-api\2.0.6\maven-plugin-api-2.0.6.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\maven-project\2.0.6\maven-project-2.0.6.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\maven-profile\2.0.6\maven-profile-2.0.6.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\maven-artifact-manager\2.0.6\maven-artifact-manager-2.0.6.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\maven-plugin-registry\2.0.6\maven-plugin-registry-2.0.6.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\maven-core\2.0.6\maven-core-2.0.6.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\wagon\wagon-file\1.0-beta-2\wagon-file-1.0-beta-2.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\maven-plugin-parameter-documenter\2.0.6\maven-plugin-parameter-documenter-2.0.6.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\wagon\wagon-http-lightweight\1.0-beta-2\wagon-http-lightweight-1.0-beta-2.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\wagon\wagon-http-shared\1.0-beta-2\wagon-http-shared-1.0-beta-2.jar;D:\java\maven\apache-maven-3.8.2\repository\jtidy\jtidy\4aug2000r7-dev\jtidy-4aug2000r7-dev.jar;D:\java\maven\apache-maven-3.8.2\repository\xml-apis\xml-apis\1.0.b2\xml-apis-1.0.b2.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\reporting\maven-reporting-api\2.0.6\maven-reporting-api-2.0.6.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\doxia\doxia-sink-api\1.0-alpha-7\doxia-sink-api-1.0-alpha-7.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\wagon\wagon-provider-api\1.0-beta-2\wagon-provider-api-1.0-beta-2.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\maven-repository-metadata\2.0.6\maven-repository-metadata-2.0.6.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\maven-error-diagnostics\2.0.6\maven-error-diagnostics-2.0.6.jar;D:\java\maven\apache-maven-3.8.2\repository\commons-cli\commons-cli\1.0\commons-cli-1.0.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\wagon\wagon-ssh-external\1.0-beta-2\wagon-ssh-external-1.0-beta-2.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\wagon\wagon-ssh-common\1.0-beta-2\wagon-ssh-common-1.0-beta-2.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\maven-plugin-descriptor\2.0.6\maven-plugin-descriptor-2.0.6.jar;D:\java\maven\apache-maven-3.8.2\repository\org\codehaus\plexus\plexus-interactivity-api\1.0-alpha-4\plexus-interactivity-api-1.0-alpha-4.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\wagon\wagon-ssh\1.0-beta-2\wagon-ssh-1.0-beta-2.jar;D:\java\maven\apache-maven-3.8.2\repository\com\jcraft\jsch\0.1.27\jsch-0.1.27.jar;D:\java\maven\apache-maven-3.8.2\repository\classworlds\classworlds\1.1\classworlds-1.1.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\maven-artifact\2.0.6\maven-artifact-2.0.6.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\maven-settings\2.0.6\maven-settings-2.0.6.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\maven-model\2.0.6\maven-model-2.0.6.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\maven-monitor\2.0.6\maven-monitor-2.0.6.jar;D:\java\maven\apache-maven-3.8.2\repository\org\codehaus\plexus\plexus-container-default\1.0-alpha-9-stable-1\plexus-container-default-1.0-alpha-9-stable-1.jar;D:\java\maven\apache-maven-3.8.2\repository\org\codehaus\plexus\plexus-utils\2.0.5\plexus-utils-2.0.5.jar;D:\java\maven\apache-maven-3.8.2\repository\org\apache\maven\shared\maven-filtering\1.1\maven-filtering-1.1.jar;D:\java\maven\apache-maven-3.8.2\repository\org\sonatype\plexus\plexus-build-api\0.0.4\plexus-build-api-0.0.4.jar;D:\java\maven\apache-maven-3.8.2\repository\org\codehaus\plexus\plexus-interpolation\1.13\plexus-interpolation-1.13.jar com.ddwei.test.service.DiGui2
0    [main] INFO  com.ddwei.test.service.DiGui2  - DiGui->main->list->:[{"call":"爷爷","children":[{"call":"爸爸","children":[{"call":"姐姐","children":[],"fatherId":"11","id":"111"},{"call":"哥哥","children":[],"fatherId":"11","id":"112"}],"fatherId":"1","id":"11"},{"call":"姑姑","children":[],"fatherId":"1","id":"12"}],"fatherId":"","id":"1"},{"call":"二爷","children":[{"call":"堂叔","children":[{"call":"堂妹","children":[],"fatherId":"21","id":"211"}],"fatherId":"2","id":"21"}],"fatherId":"","id":"2"}]
79   [main] INFO  com.ddwei.test.service.DiGui2  - DiGui->main->remotList->:[{"call":"爷爷","children":[{"call":"爸爸","children":[{"call":"姐姐","children":[],"fatherId":"11","id":"111"},{"call":"哥哥","children":[],"fatherId":"11","id":"112"}],"fatherId":"1","id":"11"},{"call":"姑姑","children":[],"fatherId":"1","id":"12"}],"fatherId":"","id":"1"},{"call":"二爷","children":[{"call":"堂叔","children":[{"call":"堂妹","children":[],"fatherId":"21","id":"211"}],"fatherId":"2","id":"21"}],"fatherId":"","id":"2"}]
95   [main] INFO  com.ddwei.test.service.DiGui2  - DiGui->main->outDtoList1->:[{"call":"爷爷","children":[{"call":"爸爸","children":[{"call":"姐姐","children":[],"id":"111","parentId":"11"},{"call":"哥哥","children":[],"id":"112","parentId":"11"}],"id":"11","parentId":"1"},{"call":"姑姑","children":[],"id":"12","parentId":"1"}],"id":"1","parentId":""},{"call":"二爷","children":[{"call":"堂叔","children":[{"call":"堂妹","children":[],"id":"211","parentId":"21"}],"id":"21","parentId":"2"}],"id":"2","parentId":""}]
95   [main] INFO  com.ddwei.test.service.DiGui2  - DiGui->main->outDtoList2->:[{"call":"爷爷","children":[{"call":"爸爸","children":[{"call":"姐姐","children":[],"id":"111","parentId":"11"},{"call":"哥哥","children":[],"id":"112","parentId":"11"}],"id":"11","parentId":"1"},{"call":"姑姑","children":[],"id":"12","parentId":"1"}],"id":"1","parentId":""},{"call":"二爷","children":[{"call":"堂叔","children":[{"call":"堂妹","children":[],"id":"211","parentId":"21"}],"id":"21","parentId":"2"}],"id":"2","parentId":""}]

Process finished with exit code 0

6　　　　应用

6.1　　　　应用 list和map的应用

ArrayList list = new ArrayList();
        HashMap sSendMap2 = new HashMap();
        sSendMap2.put("connectType", "");//联系人类型
        sSendMap2.put("linkmanName", "");//联系人姓名
        sSendMap2.put("connectGender", "");//联系人性别
        sSendMap2.put("conIdentType", "");//联系人证件种类
        sSendMap2.put("conIdentNo", "");//联系人证件号码
        sSendMap2.put("contmethType", "");//联系方式
        sSendMap2.put("contmethInfo", "");//联系方式内容
        sSendMap2.put("validFlag", "");//是否有效
        list.add(sSendMap2);
        sSendMap.put("MCiOrgLinkman", list);

ArrayList list = sRecMap.get("list");

StringBuffer sb = new StringBuffer();

HashMap tempMap = null;

for(int i=0;i<list.size();i++){

tempMap = (HashMap)list.get(i);

sb.append(temp.get("aaa").toString()+",");

sb.append(temp.get("bbb").toString()+"@");

}

String result = sb.toString();

6.2　　　　应用数组和集合之间的转变

Arrays.asList(arr).contains(name);

//我可以实现的功能是把String数组转变成一个list，观察这个list中是否包含特定的字符串，这个在Ajax01中有应用

asList(arr)返回一个受指定数组支持的固定大小的列表。

util类包含用来操作数组（比如排序和搜索）的各种方法。此类还包含一个允许将数组作为列表来查看的静态工厂。

6.3　　　　jdk8　　常见应用

package com.company;

import java.util.*;

import java.util.stream.Collectors;

public class Test1 {

    public static void main(String[] args) {

        List<User> userList = new ArrayList<>();


        userList.add(new User("1","李大锤",23,"南京"));
        userList.add(new User("2","张无忌",18,"西安"));
        userList.add(new User("3","带头大哥",36,"杭州"));  //id相同，其他数据不同
        userList.add(new User("3","333",99,"杭州"));  //id相同，其他数据不同
        userList.add(new User("3","刘德华",26,"苏州"));
        userList.add(new User("4","郭靖",33,"上海"));
        userList.add(new User("1","李大锤",23,"南京"));    //id相同，其他数据也相同

        //1     常规方法
        //1.1   去重：根据userid去重，只取第一条
        userList = userList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(User::getUserid))), ArrayList::new));
        System.out.println(userList);
　　　　　
　　　　 //1.2　　 list内部处理，不需要list结果
       userList.foreach(e-{});

        //2     互转
        //2.1   组装成String
        System.out.println(userList.stream().map(User::getName).collect(Collectors.joining("-")));

        //2.2   分组
        //2.2.1 list转map<String,Object>1
        Map<String,User> studentDtoMap = Optional.ofNullable(userList).map(
                e->{
                    return e.stream().collect(
                            Collectors.groupingBy(User::getUserid,Collectors.collectingAndThen(Collectors.reducing(
                                    (e1,e2)->
                                            e1.getThree().compareTo(e2.getThree())>=0?e1:e2),Optional::get
                            )));
                }
        ).orElse(new HashMap<>());
        System.out.println(studentDtoMap);


        //2.2.2 map转list
        userList = new ArrayList<>(studentDtoMap.values());
        System.out.println(userList);

        //2.2.3 list转map2<String,List>
        Map<String,List<User>> studentDtoMap2 = userList.stream().collect(Collectors.groupingBy(User::getUserid));
        System.out.println(studentDtoMap2);
    }
}

7　　　　理论

7.1　　　　区别 list和set的区别

list 有序，不唯一，

set 无序，唯一 set的应用场合（如vip会员登陆时，页面显示vip用户名）y12yimai项目中

posted on 2015-09-03 10:32 菜鸟乙阅读(592) 评论(0) 编辑收藏举报

刷新页面返回顶部

1 集合List

1.1 遍历

1.2 三种调用形式的使用场景

1.3 jdk8新特性

1.4 其他方法

1.5 结束for循环，continu,break，return的区别

2 集合Map

2.1 map之put方法1

2.2 map之put方法2

2.3 map中的entry

3 集合Set

4 数组

5 递归

5.1 递归List

6 应用

6.1 应用 list和map的应用

6.2 应用 数组和集合之间的转变

6.3 jdk8 常见应用

7 理论

7.1 区别 list和set的区别