如何将元素添加到 Object，List 类型的哈希映射中。
huangapple
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英文:

How to add element to hashmap of Object,List<Object>

问题

import java.util.List;
import java.util.Map;
import java.util.HashMap;

public class Test {
    public static void main(String[] args) {
        List<Object[]> result = dao.getServiceParam();
        Map<Service, List<Parameter>> mapList = new HashMap<Service, List<Parameter>>();

        if (!result.isEmpty()) {
            for (int i = 0; i < result.size(); i++) {
                Object[] line = result.get(i);
                if (line[0] != null) {
                    int serviceId = ((BigDecimal) line[0]).intValue();
                    int paramId = ((BigDecimal) line[1]).intValue();
                    String type = (String) line[2];

                    Service service = new Service(serviceId);
                    Parameter parameter = new Parameter(paramId, type);

                    if (!mapList.containsKey(service)) {
                        mapList.put(service, new ArrayList<Parameter>());
                    }
                    mapList.get(service).add(parameter);
                }
            }
        }
    }
}

class Service {
    private int id;

    public Service(int id) {
        this.id = id;
    }

    // Getters + Setters
}

class Parameter {
    private int id;
    private String type;

    public Parameter(int id, String type) {
        this.id = id;
        this.type = type;
    }

    // Getters + Setters
}
英文:

I have a list from dao, I want to put this list in a HashMap<Service,List<Paramter>>, my list can contain a service which have multiple parameters like the serviceId=3. In my final HashMap, the result looks like : {Service 1=[100,A],Service 2=[101,A],Service 3=[Parameter[102,B],Parameter[103,B],Parameter[104,C]]}.

serviceId   paramId   type
 1            100      A
 2            101      A
 3            102      B
 3            103      B
 3            104      C

Service.java

private int id;
//Getters+Setters

Parameter.java

private int id;
private String type;
//Getters+Setters

Test.java

 List result = dao.getServiceParam();
HashMap&lt;Service,List&lt;Parameter&gt;&gt; mapList = new HashMap&lt;Service, List&lt;Parameter&gt;&gt;();   
if(!result.isEmpty()) {             
for (int i=0; i&lt; result.size(); i++) {
    Object[] line = (Object[])result.get(i);        
    if ((BigDecimal) line[0]!=null) {
                   
    }
    }
    }

答案1

得分: 0

if (((BigDecimal) line[0] != null) && (line.length > 2)) {
    Service serv = new Service((Integer) line[0]);
    Parameter param = new Parameter((Integer) line[1], (String) line[2]);
    List<Parameter> paramList = mapList.get(serv);
    if (paramList == null) {
        paramList = new LinkedList<Parameter>();
    }

    paramList.add(param);

    mapList.put(serv, paramList);
}
英文: 
if ((BigDecimal) line[0]!=null &amp;&amp; line.length&gt;2) {
   
    Service serv = new Service((Integer) line[0]);
    Parameter param = new Parameter((Integer)line[1],(String) line[2]);
    List&lt;Parameter&gt; paramList=mapList.get(serv);
    if (paramList==null){
        paramList = new LinkedList&lt;Parameter&gt;();
    }

    paramList.add(param);

    mapList.put(serv, paramList);
}

You can replace your empty if with the code above.
This should serve your purpose I believe. but to run the above code you should meet below conditions.

  1. your Parameter and Service class should have a constructor.
  2. you should have overridden the hashcode and equals methods based on id attribute of Service class
  3. If you expect null at any of the field. Please handle that.

huangapple
  • 本文由 发表于 2020年4月7日 04:09:21
  • 转载请务必保留本文链接：https://java.coder-hub.com/61068125.html
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