Java中浅拷贝和深拷贝

在Java中，拷贝对象可以通过浅拷贝（Shallow Copy）和深拷贝（Deep Copy）实现。浅拷贝只复制对象的引用，而不复制对象本身。深拷贝则复制对象及其所有引用的对象，创建一个完全独立的副本。

浅拷贝

浅拷贝是指复制对象的引用，而不是对象本身。对于对象内部的引用类型字段，浅拷贝会共享同一个引用。

浅拷贝示例

class Address implements Cloneable {
    String city;

    Address(String city) {
        this.city = city;
    }

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

    @Override
    public String toString() {
        return city;
    }
}

class Person implements Cloneable {
    String name;
    int age;
    Address address;

    Person(String name, int age, Address address) {
        this.name = name;
        this.age = age;
        this.address = address;
    }

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

    @Override
    public String toString() {
        return "Person{name='" + name + "', age=" + age + ", address=" + address + '}';
    }
}

public class ShallowCopyExample {
    public static void main(String[] args) throws CloneNotSupportedException {
        Address address = new Address("New York");
        Person person1 = new Person("John", 25, address);
        Person person2 = (Person) person1.clone();

        System.out.println("Before modifying address:");
        System.out.println("Person 1: " + person1);
        System.out.println("Person 2: " + person2);

        person2.address.city = "San Francisco";

        System.out.println("After modifying address:");
        System.out.println("Person 1: " + person1);
        System.out.println("Person 2: " + person2);
    }
}

代码说明

1. Address 类：包含一个 city 字段，实现 Cloneable 接口，并重写 clone 方法。
2. Person 类：包含 name、age 和 address 字段，实现 Cloneable 接口，并重写 clone 方法。
3. ShallowCopyExample 类：展示了浅拷贝的效果。修改 person2 的 address 后，person1 的 address 也会受到影响，因为它们共享同一个 Address 对象。

深拷贝

深拷贝是指复制对象及其所有引用的对象，创建一个完全独立的副本。对于对象内部的引用类型字段，深拷贝会递归地复制它们。

深拷贝示例

class Address implements Cloneable {
    String city;

    Address(String city) {
        this.city = city;
    }

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

    @Override
    public String toString() {
        return city;
    }
}

class Person implements Cloneable {
    String name;
    int age;
    Address address;

    Person(String name, int age, Address address) {
        this.name = name;
        this.age = age;
        this.address = address;
    }

    @Override
    protected Object clone() throws CloneNotSupportedException {
        Person cloned = (Person) super.clone();
        cloned.address = (Address) address.clone();
        return cloned;
    }

    @Override
    public String toString() {
        return "Person{name='" + name + "', age=" + age + ", address=" + address + '}';
    }
}

public class DeepCopyExample {
    public static void main(String[] args) throws CloneNotSupportedException {
        Address address = new Address("New York");
        Person person1 = new Person("John", 25, address);
        Person person2 = (Person) person1.clone();

        System.out.println("Before modifying address:");
        System.out.println("Person 1: " + person1);
        System.out.println("Person 2: " + person2);

        person2.address.city = "San Francisco";

        System.out.println("After modifying address:");
        System.out.println("Person 1: " + person1);
        System.out.println("Person 2: " + person2);
    }
}

代码说明

1. Address 类：与浅拷贝示例中相同，实现 Cloneable 接口并重写 clone 方法。
2. Person 类：在 clone 方法中，对 address 字段进行深拷贝（递归调用 address 的 clone 方法）。
3. DeepCopyExample 类：展示了深拷贝的效果。修改 person2 的 address 后，person1 的 address 不会受到影响，因为它们拥有独立的 Address 对象。

通过这些示例代码，可以看到浅拷贝和深拷贝在实现和效果上的差异。浅拷贝会共享对象的引用，而深拷贝则创建独立的对象副本。