在HashMap中插入后修改了密钥对象

Question

我从Excel中读取一个表并将数据传递到hasp映射中。但是，看起来插入后，键中使用的元素之一会被覆盖。我无法弄清楚出了什么问题。如果有人可以帮助我，我真的很感激。

// AssetCity类定义

public class AssetCity{

    public int asset;

    private int city; 

//constructors

//setters

// hashCode and Equals methods

在main函数中，我首先阅读excel表并创建我的地图。

XSSFSheet _pi = myWorkbook.getSheet("pi"); //get the sheet              

Map<AssetCity, Integer> pi = new HashMap<AssetCity, Integer>(); //create map            

    for(int i = _pi.getFirstRowNum() + 1 ; i <= _pi.getLastRowNum(); i++){              

        AssetCity pair = new AssetCity();   

        Row ro = _pi.getRow(i); //get each row

    for(int j = ro.getFirstCellNum()+1; j <= ro.getLastCellNum()-1;  j++) {

    Cell ce = ro.getCell(j); //go through each column 

    pair.setAssetCity(i, j); //create the key that will be inserted

        int val = (int) ce.getNumericCellValue(); // get the cell value                      

      // System.out.println(pair.toString()+ " "+ val);

    pi.put(pair, val); // insert into the map

        }                       

}

当我System.out.println(pair.toString()+ " "+ val);在插入操作之前使用时，我得到的内容如下所示，这是正确的并且与我在Excel中的值匹配。

asset_city [asset=1, city=1] 0

asset_city [asset=1, city=2] 0

asset_city [asset=1, city=3] 0

.....

asset_city [asset=5, city=3] 1

asset_city [asset=5, city=4] 0              

现在，在完成for循环后，我迭代了地图中的所有元素。

Iterator<Map.Entry<AssetCity,Integer>> itr1 = pi.entrySet().iterator();

    while(itr1.hasNext())

        {

          Map.Entry<AssetCity,Integer> entry = itr1.next();                 

                  System.out.println(entry.getKey().toString() + " = " + entry.getValue());

现在，正如您所看到的，键中的城市值看起来都是一样的。

asset_city [asset=2, city=4] = 0

asset_city [asset=3, city=4] = 0

asset_city [asset=4, city=4] = 0

asset_city [asset=5, city=4] = 0

asset_city [asset=1, city=4] = 0

asset_city [asset=2, city=4] = 1

asset_city [asset=3, city=4] = 0

asset_city [asset=4, city=4] = 0

asset_city [asset=1, city=4] = 0

Answer 1

您正在AssetCity为一行中的每个单元格覆盖同一对象中的数据。修复，声明和初始化AssetCity内部循环内的对象而不是外部循环

Answer 2

因为AssetCity对是在内部循环之外创建的，所以在“j”循环的每次迭代中都会更新该创建的对。也许你想在内部循环中创建一个AssetCity对的新实例，就像下面的代码片段一样。这意味着它是内部'j'循环的每次迭代的新实例。XSSFSheet&nbsp;_pi&nbsp;=&nbsp;myWorkbook.getSheet("pi");&nbsp;//get&nbsp;the&nbsp;sheet&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Map<AssetCity,&nbsp;Integer>&nbsp;pi&nbsp;=&nbsp;new&nbsp;HashMap<AssetCity,&nbsp;Integer>();&nbsp;//create&nbsp;map&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; for(int&nbsp;i&nbsp;=&nbsp;_pi.getFirstRowNum()&nbsp;+&nbsp;1&nbsp;;&nbsp;i&nbsp;<=&nbsp;_pi.getLastRowNum();&nbsp;i++){&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;Row&nbsp;ro&nbsp;=&nbsp;_pi.getRow(i);&nbsp;//get&nbsp;each&nbsp;row &nbsp;&nbsp;&nbsp;&nbsp;for(int&nbsp;j&nbsp;=&nbsp;ro.getFirstCellNum()+1;&nbsp;j&nbsp;<=&nbsp;ro.getLastCellNum()-1;&nbsp;&nbsp;j++)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Cell&nbsp;ce&nbsp;=&nbsp;ro.getCell(j);&nbsp;//go&nbsp;through&nbsp;each&nbsp;column&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;AssetCity&nbsp;pair&nbsp;=&nbsp;new&nbsp;AssetCity();&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;pair.setAssetCity(i,&nbsp;j);&nbsp;//create&nbsp;the&nbsp;key&nbsp;that&nbsp;will&nbsp;be&nbsp;inserted &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int&nbsp;val&nbsp;=&nbsp;(int)&nbsp;ce.getNumericCellValue();&nbsp;//&nbsp;get&nbsp;the&nbsp;cell&nbsp;value&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;//&nbsp;System.out.println(pair.toString()+&nbsp;"&nbsp;"+&nbsp;val); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;pi.put(pair,&nbsp;val);&nbsp;//&nbsp;insert&nbsp;into&nbsp;the&nbsp;map &nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}