如何复制不受原始ArrayList更改影响的ArrayList？ [英] How to copy an ArrayList that cannot be influenced by the original ArrayList changes?

问题描述

我一直在我的一个项目上使用ArrayLists，我需要创建一个默认的ArrayList，以便可以随时重置原始列表。因此，我复制了原始的ArrayList来创建默认的ArrayList。但是，每当我修改原始文件上的内容时，它也会更改默认文件。我如何使副本静态且不可更改？

这是我的代码：（用葡萄牙语）

  private ArrayList< Compartimento> listaCompartimentos; 
 private ArrayList< Compartimento> listaCompartimentosDEFAULT; 
 
 public Simulador（）{
 this.listaCompartimentos = new ArrayList<>（）; 
 this.listaCompartimentosDEFAULT = new ArrayList<>（）; 
} 
 
 //数组的复制
 public void gravarListaDefault（）{
 this.listaCompartimentosDEFAULT =（ArrayList< Compartimento>）listaCompartimentos.clone（）; 
} 
  

注意：我不知道这可能是其背后的原因，但是ArrayList listaCompartimentos具有listaEquipamentos。对于每个 Compartimento，都有一个ArrayList listaEquipamentos。

解决方案

克隆表示您有2个不同的列表，但是它们的内容是相同。如果更改第一个列表中的对象的状态，则它将在第二个列表中更改。

使用复制构造函数，并避免 clone（）：

应该避免为数组列表使用 new ArrayList（originalList）

Clone（），因为即使创建了新实例，其中包含相同元素。因此，在列表上更改的元素将在第二个元素上更改。

下面的代码将创建带有新元素的新实例。

  ArrayList< Object> clone =新的ArrayList< Object>（）; 
 for（对象o：originalList）
 clone.add（o.clone（））; 
  

I've been using ArrayLists on a project of mine, and I need to create a default ArrayList so I can reset the original one whenever I want. So, I copy the original ArrayList to create the default one. However, whenever I modify something on the original, it also changes the default one. How can I make the copy "static" and unchangeable?

Here is my code: (It's in portuguese)

private ArrayList<Compartimento> listaCompartimentos;
private ArrayList<Compartimento> listaCompartimentosDEFAULT;

public Simulador() {
        this.listaCompartimentos = new ArrayList<>();
        this.listaCompartimentosDEFAULT=new ArrayList<>();
    }

//Copy of the array
public void gravarListaDefault(){
        this.listaCompartimentosDEFAULT=(ArrayList<Compartimento>)listaCompartimentos.clone();
    }

Note: I don't know if it can be the reason behind it, but the ArrayList listaCompartimentos has a listaEquipamentos. For each "Compartimento" there is an ArrayList "listaEquipamentos".

解决方案

Cloning means you have 2 different lists, but their contents are the same. If you change the state of an object inside the first list, it will change in the second list.

Use the copy-constructors and avoid clone() :

new ArrayList(originalList)

Clone() for arraylists should be avoided because even if it creates a new instance, it holds the same elements. So an element which is changed on a list will be changed on the second one.

The code below will create a new instance with new elements.

ArrayList<Object> clone = new ArrayList<Object>();
for(Object o : originalList)
clone.add(o.clone());

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