浅拷贝与深拷贝

Posted on 2023-04-23 Symbols count in article: 5.3k Reading time ≈ 5 mins.

在工作开发中，我们有时候需要将一份原始数据复制成一份新数据，再对新数据进行部分修改，这里就引出浅拷贝与深拷贝两个概念。

需要注意的是，浅拷贝和深拷贝是编程中的概念，它们并不局限于某一种语言，每种语言都有自己的浅拷贝/深拷贝方式。

什么是浅拷贝？

对于基本类型数据，浅拷贝复制了数据本身，而对于对象类型数据，浅拷贝只复制了对象的引用，而不是对象本身
因此，如果修改了浅拷贝后数据中的对象，那么原始数据中的对象也会受到影响

什么是深拷贝

对于基本类型数据，深拷贝复制了数据本身，而对于对象类型数据，深拷贝会递归复制对象的所有元素，包括对象类型
深拷贝后的数据是完全和原始数据独立的，因此对它进行任何操作都是安全的

Java中实现浅拷贝

使用Object.clone()方法

代码示例

public class Order implements Cloneable {
    private String orderName;
    private Long orderNo;
    private Address address;

    // 省略getter/setter

    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

public class Address {
    private String country;
    private String province;
    private String city;
    private String district;
    private String detailAddress;

    // 省略getter/setter
}

public class TestCopy {
    public static void main(String[] args) throws CloneNotSupportedException {
        Address address = new Address();
        address.setCountry("中国");
        address.setProvince("浙江省");
        address.setCity("杭州市");
        address.setDistrict("西湖区");
        address.setDetailAddress("凤起路");

        Order order = new Order();
        order.setOrderName("双十一好物订单");
        order.setOrderNo(202300156L);
        order.setAddress(address);

        System.out.println("order: " + order);
        System.out.println("address: " + address);
        System.out.println("detailAddress: " + address.getDetailAddress());

        Order copyOrder = (Order) order.clone();
        
        System.out.println("copyOrder: " + copyOrder);
        System.out.println("copyAddress: " + copyOrder.getAddress());

        copyOrder.getAddress().setDetailAddress("武林广场");
        System.out.println("detailAddress: " + address.getDetailAddress());
    }
}

运行结果

order: com.codecho.copy.Order@677327b6
address: com.codecho.copy.Address@14ae5a5
detailAddress: 凤起路
copyOrder: com.codecho.copy.Order@7f31245a
copyAddress: com.codecho.copy.Address@14ae5a5
detailAddress: 武林广场

==可以看出，使用Object.clone()方法复制出了一个新的Order对象，但是Order对象内部的Address还是原来的Address对象，并且对新Order对象内部Address进行修改会影响到原Address对象，说明Object.clone()方法只是拷贝了对象的引用，并没有拷贝对象本身。==

使用apache或spring提供的BeanUtils工具类

代码示例

<dependency>
    <groupId>commons-beanutils</groupId>
    <artifactId>commons-beanutils</artifactId>
    <version>1.9.4</version>
</dependency>

public class TestCopy {

    public static void main(String[] args) throws InvocationTargetException, IllegalAccessException {
        Address address = new Address();
        address.setCountry("中国");
        address.setProvince("浙江省");
        address.setCity("杭州市");
        address.setDistrict("西湖区");
        address.setDetailAddress("凤起路");

        Order order = new Order();
        order.setOrderName("双十一好物订单");
        order.setOrderNo(202300156L);
        order.setAddress(address);

        System.out.println("order: " + order);
        System.out.println("address: " + address);
        System.out.println("detailAddress: " + address.getDetailAddress());

        Order copyOrder = new Order();
        BeanUtils.copyProperties(copyOrder, order);

        System.out.println("copyOrder: " + copyOrder);
        System.out.println("copyAddress: " + copyOrder.getAddress());

        copyOrder.getAddress().setDetailAddress("武林广场");
        System.out.println("detailAddress: " + address.getDetailAddress());
    }

}

运行结果

order: com.codecho.copy.Order@330bedb4
address: com.codecho.copy.Address@2503dbd3
detailAddress: 凤起路
copyOrder: com.codecho.copy.Order@685f4c2e
copyAddress: com.codecho.copy.Address@2503dbd3
detailAddress: 武林广场

==和Object.clone()方法一样，BeanUtils.copyProperties()方法也是浅拷贝==

Java中实现深拷贝

序列化和反序列化

代码示例

==注意：Order和Address需要实现Serializable接口==

public class Order implements Serializable {
    ...
}

public class Address implements Serializable {
    ...
}

public static void main(String[] args) throws IOException, ClassNotFoundException {
    Address address = new Address();
    address.setCountry("中国");
    address.setProvince("浙江省");
    address.setCity("杭州市");
    address.setDistrict("西湖区");
    address.setDetailAddress("凤起路");

    Order order = new Order();
    order.setOrderName("双十一好物订单");
    order.setOrderNo(202300156L);
    order.setAddress(address);

    System.out.println("order: " + order);
    System.out.println("address: " + address);
    System.out.println("detailAddress: " + address.getDetailAddress());

    Order copyOrder = deepCopy(order);
	
    System.out.println("copyOrder: " + copyOrder);
    System.out.println("copyAddress: " + copyOrder.getAddress());

    copyOrder.getAddress().setDetailAddress("武林广场");
    System.out.println("detailAddress: " + address.getDetailAddress());
}


public static Order deepCopy(Order source) throws IOException, ClassNotFoundException {
    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    ObjectOutputStream out = new ObjectOutputStream(outputStream);
    out.writeObject(source);

    ByteArrayInputStream inputStream = new ByteArrayInputStream(outputStream.toByteArray());
    ObjectInputStream in = new ObjectInputStream(inputStream);

    Order copy = (Order) in.readObject();
    return copy;
}

运行结果

order: com.codecho.copy.Order@330bedb4
address: com.codecho.copy.Address@2503dbd3
detailAddress: 凤起路
copyOrder: com.codecho.copy.Order@7e6cbb7a
copyAddress: com.codecho.copy.Address@7c3df479
detailAddress: 凤起路