Java 深度复制对象：从基础到实战

在 Java 编程中，对象的复制是一个常见的需求。然而，简单的复制操作（如直接赋值）只会复制对象的引用，而不是创建一个新的对象。这意味着两个引用会指向同一个内存地址，修改其中一个对象会影响另一个对象。为了解决这个问题，我们需要实现对象的深度复制。本文将详细介绍如何在 Java 中实现对象的深度复制，并通过具体代码示例帮助你更好地理解和应用这一技术。

一、深度复制的概念

深度复制是指创建一个新对象，并将原对象的所有字段值复制到新对象中。如果字段是基本数据类型，则直接复制其值；如果字段是引用类型，则需要递归地创建该引用对象的深度副本。这样可以确保新对象与原对象在内存中完全独立，修改其中一个不会影响另一个。

二、实现深度复制的方法

1. 使用序列化

Java 的序列化机制可以将对象转换为字节流，然后再将字节流还原为对象。这一过程实际上创建了一个对象的深度副本。

import java.io.*;public class DeepCloneExample implements Serializable {private String name;private TransientData transientData;public DeepCloneExample(String name, TransientData transientData) {this.name = name;this.transientData = transientData;}public String getName() {return name;}public TransientData getTransientData() {return transientData;}@Overridepublic String toString() {return "DeepCloneExample{" +"name='" + name + '\'' +", transientData=" + transientData +'}';}public static DeepCloneExample deepClone(DeepCloneExample obj) throws IOException, ClassNotFoundException {ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();ObjectOutputStream objectOutputStream = new ObjectOutputStream(byteArrayOutputStream);objectOutputStream.writeObject(obj);objectOutputStream.close();ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(byteArrayOutputStream.toByteArray());ObjectInputStream objectInputStream = new ObjectInputStream(byteArrayInputStream);DeepCloneExample clonedObj = (DeepCloneExample) objectInputStream.readObject();objectInputStream.close();return clonedObj;}
}class TransientData implements Serializable {private int value;public TransientData(int value) {this.value = value;}@Overridepublic String toString() {return "TransientData{" +"value=" + value +'}';}
}

2. 手动实现深度复制

对于某些复杂对象，手动实现深度复制可能更高效。这需要为每个需要复制的对象编写自定义的 clone 方法。

public class DeepCopyExample {private int id;private String name;private Address address;public DeepCopyExample(int id, String name, Address address) {this.id = id;this.name = name;this.address = address;}public DeepCopyExample deepCopy() {Address copiedAddress = new Address(this.address.getStreet(), this.address.getCity());return new DeepCopyExample(this.id, this.name, copiedAddress);}@Overridepublic String toString() {return "DeepCopyExample{" +"id=" + id +", name='" + name + '\'' +", address=" + address +'}';}public static void main(String[] args) {Address originalAddress = new Address("123 Main St", "Anytown");DeepCopyExample original = new DeepCopyExample(1, "Example", originalAddress);DeepCopyExample copy = original.deepCopy();System.out.println("Original: " + original);System.out.println("Copy: " + copy);original.getAddress().setCity("New City");System.out.println("After changing original's address city:");System.out.println("Original: " + original);System.out.println("Copy: " + copy);}
}class Address {private String street;private String city;public Address(String street, String city) {this.street = street;this.city = city;}public String getStreet() {return street;}public void setStreet(String street) {this.street = street;}public String getCity() {return city;}public void setCity(String city) {this.city = city;}@Overridepublic String toString() {return "Address{" +"street='" + street + '\'' +", city='" + city + '\'' +'}';}
}