添加新的键值对将替换HashMap中的其他键值

Question

因此，我有一个hashmap ，它存储每个字符串的arraylist。但是当我用ArrayList的新值添加另一对时，其他键值将被替换。因此，不同键的所有值都是相同的。

public class Reports{
    
    private ArrayList<Resource> resourceList;
    private HashMap<String,ArrayList<Resource>> consolidatedAttendance = new HashMap<String,ArrayList<Resource>>(); 
    
    public void readReport(String reportFile){
        //initialized with resources from config file
        ArrayList<Resource> repResourceList = new ArrayList<Resource>(getResourceList());

        try (BufferedReader br = new BufferedReader(new FileReader(reportFile))) {
            String line;
            line = br.readLine(); // disregards first line (columns)
            while ((line = br.readLine()) != null) {
                
                if(line.length()==0){
                    break;
                }
                
                //store each resource status in resourceList
                String[] values = line.split(",");      
                String resourceName = values[1], resourceStatus = values[2];
                int resourceIndex = indexOfResource(resourceList, resourceName);
                // to add validation 
                if(resourceIndex!=-1){
                    repResourceList.get(resourceIndex).setStatus(resourceStatus);
                }
                
            }
        }catch(IOException e){
            e.printStackTrace();
        }
        
        
        //get Date
        String reportFilename = reportFile.substring(0, reportFile.indexOf("."));
        String strDate = reportFilename.substring(reportFilename.length()-9);
        consolidateRecords(strDate, new ArrayList<Resource>(repResourceList));
        
    }
    
    
    public void consolidateRecords(String strDate, ArrayList<Resource> repResourceList){
        //consolidate records in hashmap
        consolidatedAttendance.put(strDate, repResourceList);
        
        // test print
        
        for (String key: consolidatedAttendance.keySet()){
            ArrayList<Resource> resources = consolidatedAttendance.get(key);  
            for(Resource resource: resources){
                System.out.println(key+": "+resource.getNickname()+" "+resource.getEid()+" "+resource.getStatus());
            }
        } 
    }
}

添加的第一个键：

"21-Dec-20": John Working
"21-Dec-20": Alice Working
"21-Dec-20": Jess Working

对于第二个键，列表中有不同。但是，当添加第二个键（在put（）方法之后）时，第一个键的值已经被替换。

"21-Dec-20": John SL
"21-Dec-20": Alice Working
"21-Dec-20": Jess SL

"28-Dec-20": John SL
"28-Dec-20": Alice Working
"28-Dec-20": Jess SL

Answer 1

您的映射的值是列表，其元素与GetResourcelist()返回的列表的元素相同。创建列表的副本（两次）并不能改变这一点。

如果每次调用GetResourcelist()返回包含相同实例的列表，则映射中的所有键都将与包含相同实例的不同列表关联。