java - 如何在不指向 Java 源列表中的对象的情况下复制 ArrayList？

Question

这个问题已经有答案了:

How to clone ArrayList and also clone its contents? (21 个回答)

已关闭 3 年前。

我的问题是我想复制其中包含对象的 ArrayList。
之后，我想更改“复制列表”中的对象，而不更改源列表中的对象。

我已经尝试过:

ArrayList<..> copy = new ArrayList<..>(sourceList); 
Collections.copy(dest, src);

更具体的问题在这里:

ArrayList<Exon> regions1 = new ArrayList<>();
regions1.add(r1);
regions1.add(r2);
regions1.add(r3);
System.out.println("Reg 1");
for (Exon e : regions1) {
    System.out.println(e.getStart());
}

ArrayList<Exon> copy = new ArrayList<>(regions1);
System.out.println("Copy");
for (Exon e : copy) {
    e.setStart(2);
    System.out.println(e.getStart());
}
System.out.println("Reg 1 - untouched");
for (Exon e : regions1) {
    System.out.println(e.getStart());
}

我得到的输出是:

Reg 1
5
15
100
Copy
2
2
2
Reg 1
2
2
2

我想要的输出是:

Reg 1
5
15
100
Copy
2
2
2
Reg 1
5
15
100

Answer 1

您只需为 Exon 创建一个复制构造函数即可。然后在 foreach 中，您必须传递 new Exon 对象。(with start=2)

A copy constructor: That's helpful when we want to copy a complex object that has several fields, or when we want to make a deep copy of an existing object.

<小时/>

1- Create copy constructor for Exon

public class Exon {

    private int start;

    //Copy constructor
    public Exon(Exon exon) {
        this.start = exon.getStart();
    }

    //Main Constructor and Getters and Setters

   }

2- Create a copy from main list

 List<Exon> CopyList = mainList.stream().map(exon -> {
        Exon copyExon = new Exon();
        copyExon.setStart(2);
        return new Exon(copyExon);
    }).collect(Collectors.toList());

我按如下方式编写了您的代码:

public static void main(String[] args) {

        //Initialize
        ArrayList<Exon> mainList = new ArrayList<>();
        Exon r1 = new Exon();
        r1.setStart(5);
        Exon r2 = new Exon();
        r2.setStart(10);
        Exon r3 = new Exon();
        r3.setStart(15);
        mainList.add(r1);
        mainList.add(r2);
        mainList.add(r3);

        //Print mainList
        System.out.println("Reg 1");
        for (Exon e : mainList) {
            System.out.println(e.getStart());
        }

        //Copy the mainList (I changed your foreach)
        List<Exon> copyList = mainList.stream().map(exon -> {

            //Create New Exon
            Exon copyExon = new Exon(exon);
            copyExon.setStart(2);
            return copyExon ;

        }).collect(Collectors.toList());

        //Print copyList
        System.out.println("Copy");
        for (Exon e : copyList) {
            System.out.println(e.getStart());
        }

        //Print mainList
        System.out.println("Reg 1 - untouched");
        for (Exon e : mainList) {
            System.out.println(e.getStart());
        }
    }

结果:

Reg 1
5
10
15
Copy
2
2
2
Reg 1 - untouched
5
10
15

This link可能对复制构造函数有用