错误 saving/allocation/setting 个变量

Question

我的代码有问题，我没有发现错误，一定是小问题。

// This list is filled with Objects of Matcher
ArrayList<Matcher > fullListForBundle = new ArrayList<>();

// making a new ArrayList
ArrayList<Matcher> bundlelist = new ArrayList<>();

// making a new object
Matcher currentBundle = new Matcher();

// Searching trough an Arraylist of Objects.
for (Matcher current : stockDataCompleteWithBundle)
{
    // Get an Identifier
    String han = current.getThirdColumn();
    // Search through an other list to match identifier
    for (int i = 0; i < fullListForBundle.size(); i++)
    {
        // If identifier matches then do:
        if (fullListForBundle.get(i).getFifteenthColumn().equals(han))
        {
            // I want to get the right object and save it in currentBundle
            currentBundle = fullListForBundle.get(i);

            // !!! Here begins my problem !!!

            // Then I want to change two Strings in that particular Object
            currentBundle.setFirstColumn(current.getFirstColumn());
            currentBundle.setThirteenthColumn(current.getSecondColumn());

            // And add that object to a new Arraylist
            bundlelist.add(currentBundle);
            }

        }
    }

我的问题是：通过设置 firstColumn 和 thirteenthColumn，更改了 fullListBundle.get(i) 对象中的数据，而不是 currentBundle 对象中的数据。我错过了什么？

Answer 1

这是因为您使用的是同一个对象。您需要获取一个克隆对象并进行更改。

currentBundle = fullListForBundle.get(i).clone()

Answer 2

当你这样做时，

currentBundle = fullListForBundle.get(i);

currentBundle 和 fullListForBundle.get(i) 都引用了堆中的同一个对象。您应该看到两者的结果相同。如果您只是想让 currentBundle 尝试更改，

 currentBundle = fullListForBundle.get(i).clone();

编辑：Object.clone() 方法具有 protected 访问权限，这意味着它对同一包中的子类和类可见。

最好有一个复制构造函数来手动复制对象。

/**
    Deep copy all the information from other to this
*/
public Matcher(Matcher other) {
   this.id = other.id;
}

Read Why a copy constructor by Josh Bloch ?

错误 saving/allocation/setting 个变量

Wrong saving/allocation/setting of variables

java

variables

arraylist

local-variables