如何使用Java中的数组成员深度复制（克隆）对象？

Question

Introduction

I have a Class Persons that contains an array of Person and functions :

function Persons() {
  this.mItems = []; // Array of Objects Person
}

Persons.prototype = {
  calculateScores : function() {
    // Do some stuff
  }
}

The Class Person has members and functions :

function Person(name) {
  this.name = name; // Name of the Person
  this.score = 0;
}

Person.prototype = {
  calculateScore : function() {
    // Do some stuff
  }
}

I want that the program does the following things :

var persons = new Persons();
var person0 = new Person("John");
var person1 = new Person("Sam");
persons.mItems.push(person0);
persons.mItems.push(person1);

// Completely clone the original Objects
clonedPersons = persons.clone(); // I am looking for a clone() function

// Modify an item in the cloned Objects
clonedPersons.mItems[0].name = "Mick";

// Check that the original Objects have not been modified
console.log(persons.mItems[0].name); // John : Not modified
console.log(clonedPersons.mItems[0].name); // Mick

Question

I want to deep copy an instance of Persons to completely duplicate the Array of Person . The Objects Person must be duplicated. The functions of the Objects must be kept.

JQuery.extend()

JQuery.extend(true, {}, persons) clones the direct members of Persons but shallow copies the Person Objects.

console.log(persons.mItems[0].name); // Mick : Where is John ?!
console.log(clonedPersons.mItems[0].name); // Mick

JSON.parse(json.stringify())

clonedPersons = JSON.parse(json.stringify(persons)) clones the Objects but remove the functions.

persons.mItems[0].calculateScore(); // Does not exists !!!

Thank you for your answers.

Answer 1

If you're dealing with custom classes, you're going to want to implement custom clone methods. Generally, in this context, I'd have 2 separate clone functions, one on the Person model and one on the Persons collection.

Persons.prototype = {
  clone: function() {
    var clone = new Persons();
    clone.mItems = this.mItems.map(function(person) {
        return person.clone();
    });
    return clone;
  }
}

Person.prototype = {
  clone: function() {
    var clone = new Person(this.name);
    clone.score = this.score;
    return clone;
  }
}

The advantage to this approach is that it separates the concerns - the Person class doesn't have to know how to clone a single Person , it only has to know that Person exposes a clone method. If Person adds a new property that should be persisted in the clone, only Person needs to change.

It's generally an anti-pattern to use generic clone methods, eg from jQuery or Underscore, in this context. They'll end up cloning things you don't want, or missing things you do (eg a Person might eventually have an Address or some other object that will also need cloning).

Answer 2

You can use [].map and Object.assign :

Persons.prototype.clone = function() {
   var clone = new Persons();
   clone.mItems = this.mItems.map(function(person) {
     return Object.assign(new Person, person);
   });
   return clone;
};