深拷贝揭秘：浅拷贝之困，深拷贝之妙

2023-11-02 00:40:27

编程的世界里，深拷贝和浅拷贝的概念对于程序员来说并不陌生，它们是对象复制的两大方式。深拷贝顾名思义，就是对对象进行彻底的复制，无论是一级属性还是二级属性，都会进行复制，从而创建一个全新的对象。而浅拷贝则只复制对象的引用，而不是实际的值，因此修改浅拷贝的对象也会影响到原始对象。

浅拷贝的困境

浅拷贝的简单实现方法是直接将一个对象的引用赋值给另一个对象，这是一种非常快速的方法，但它也有一个致命的缺陷，那就是如果修改了浅拷贝的对象，原始对象也会跟着发生改变。

class Student {
    private String name;
    private Address address;

    public Student(String name, Address address) {
        this.name = name;
        this.address = address;
    }
}

class Address {
    private String street;
    private String city;

    public Address(String street, String city) {
        this.street = street;
        this.city = city;
    }
}

public class ShallowCopyExample {
    public static void main(String[] args) {
        Address address = new Address("123 Main Street", "Anytown");
        Student student1 = new Student("John Doe", address);
        Student student2 = student1; // Shallow copy

        student2.setName("Jane Doe");
        student2.getAddress().setStreet("456 Elm Street");

        System.out.println(student1.getName()); // Jane Doe
        System.out.println(student1.getAddress().getStreet()); // 456 Elm Street
    }
}

在这个例子中，student1和student2都是同一个对象的引用，因此修改student2也会影响到student1。这在某些情况下可能不是我们想要的，比如当我们需要修改一个对象而又不影响另一个对象时。

深拷贝的妙用

深拷贝可以解决浅拷贝的困境。它通过创建一个新的对象来复制原始对象，这样即使修改了深拷贝的对象，也不会影响到原始对象。

class Student {
    private String name;
    private Address address;

    public Student(String name, Address address) {
        this.name = name;
        this.address = new Address(address.getStreet(), address.getCity()); // Deep copy of address
    }
}

class Address {
    private String street;
    private String city;

    public Address(String street, String city) {
        this.street = street;
        this.city = city;
    }
}

public class DeepCopyExample {
    public static void main(String[] args) {
        Address address = new Address("123 Main Street", "Anytown");
        Student student1 = new Student("John Doe", address);
        Student student2 = new Student(student1.getName(), student1.getAddress()); // Deep copy of student1

        student2.setName("Jane Doe");
        student2.getAddress().setStreet("456 Elm Street");

        System.out.println(student1.getName()); // John Doe
        System.out.println(student1.getAddress().getStreet()); // 123 Main Street
    }
}