Java：将对象添加到对象列表中 [英] Java : Adding objects to a list of objects

问题描述

它非常简单但不知何故不起作用（奇怪!!）。

Its very simple but somehow not working (weird!!).

我有一个类类型的列表。我在for循环中将对象添加到列表中。直到添加对象一切正常，但是一旦我尝试访问列表，只显示最后一个对象的值（参考我在下面显示的输出）。这里是代码：

I have a List of a class type. I am adding objects to the list in a for loop. Up till adding object everything is Ok, but as soon as I try to access the list, only the last object's values are shown (refer to the output I have shown below). Also here is the code:

    List<myClass> myClassList = new ArrayList<myClass>();
    myClass myClassObj = new myClass();

    for(int i=0;i<someArray.length;i++){
        myClassObj.setProperty1("value1");
        myClassObj.setProperty2("value2");
        myClassObj.setProperty3("value3");
        ...
        ...Others
        ...
        System.out.println(myClassList.add(myClassObj));////////////////////////
    }

    System.out.println(myClassList.size());/////////////////////////////////////

    for(int i=0;i<myClassList.size();i++){
        System.out.println(myClassList.get(i).getProperty1());/////////////////
        .....
        .....Others
        .....
    }
    Iterator<myClass> mcItr = myClassList.iterator();
    while(mcItr.hasNext()){
        myClass obj = mcItr.next();
        System.out.println(obj.getProperty1());
        .....
        .....Others
        .....
    }

此程序的输出（如果 someArray 的大小为 5 ）：

The output of this program is (if the size of someArray is 5) :

    //'true' --> 5 times. Printed by the 'add' statement as it returns 'true' when everything is OK

    //5  --> Size of 'myClassList' this is also OK

    //Here the values corresponding to the fifth and the last object are printed and repeated 5 times. Instead of printing each objects value once. (whichever way of printing to console I may use, the result is same).

在这里，我无法弄清楚我是以错误的方式创建列表还是在错误的方式。

Here I can not figure out whether I am creating the list in a wrong way or accessing it in a wrong way.

请建议。

谢谢!!

推荐答案

填充列表时，您反复将引用添加到同一对象。要解决此问题，请将 myClassObj 初始化移至循环中：

When populating the list, you are repeatedly adding references to the same object. To fix, move the myClassObj initialization into the loop:

for(int i=0;i<someArray.length;i++){
    myClass myClassObj = new myClass(); // <---- moved this into the loop
    myClassObj.setProperty1("value1");

这将为列表的每个元素创建一个单独的对象。

This will create a separate object for every element of the list.

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