变量的保存/分配/设置错误

Question

我的代码有问题，我没有发现错误，一定是微不足道的。

// 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：通过设置第一列和第十三列，fullListBundle.get(i( 对象中的数据会发生变化，而不是当前捆绑对象。我错过了什么？

Answer 1

当你这样做时，

currentBundle = fullListForBundle.get(i);

currentBundle和fullListForBundle.get(i)都引用堆中的同一对象。您应该看到两者相同的结果。如果您只想让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。

最好有一个用于手动复制对象的复制构造函数。

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

阅读Why a copy constructor by Josh Bloch ?

Answer 2

这是因为您使用的是同一对象。 您需要获取克隆的对象并进行更改。

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