【Java基础面试题041】Java中的深拷贝和浅拷贝有什么区别？

回答重点

深拷贝：深拷贝不仅复制对象本身，还递归复制对象中所有引用的对象。这样新对象与原对象完全独立，修改新对象不会影响到原对象。即包括基本类型和引用类型，堆内的引用对象也会复制一份

浅拷贝：浅拷贝只复制对象的引用，而不复制引用指向的实际对象，也就是说，浅拷贝创建一个新对象，但它的字段（若是对象类型）指向的是原对象中的相同内存地址

深拷贝创建的新对象与原对象完全独立，任何一个对象的修改都不会影响另一个。二修改浅拷贝对象中的引用类型的字段会影响要原对象，因为它们共享相同的引用

扩展知识

图示深浅拷贝

浅拷贝实现

常见实现方式是重写Object.clone()方法，默认方法这个方法只是对对象的字段进行字段拷贝，对于基本类型的字段会复制值，对于引用类型的字段则复制引用

重写Clone()的类需要实现Cloneable接口，否则抛出异常CloneNotSupportedException

public class ShallowCopyTest {
    public static void main(String[] args) throws CloneNotSupportedException{
        ShallowCopyTest test = new ShallowCopyTest();
        Person john = test.new Person("John", 25, new ArrayList<>(Arrays.asList("电玩", "旅游")));
        Person johnCopy = (Person) john.clone();
        System.out.println(john);
        System.out.println(johnCopy);
        System.out.println(john.hobbies == johnCopy.hobbies);
    }

    class Person implements Cloneable{
        String name;
        int age;
        List<String> hobbies;

        public Person(String name, int age, List<String> hobbies) {
            this.name = name;
            this.age = age;
            this.hobbies = hobbies;
        }

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

        @Override
        public String toString(){
            return name + "已经" + age + "岁了，喜欢" + hobbies.get(0) + " 和 " + hobbies.get(1);
        }
    }
}

深拷贝实现

深拷贝可以通过递归调用clone()方法手动实现，也可以通过序列化与反序列化实现。序列化方式简单易用，但性能相对较低，尤其是在深层嵌套对象或大对象的情况下。

• 递归调用clone()实现

public class DeepCopyTest {
    public static void main(String[] args) throws CloneNotSupportedException {
        DeepCopyTest test = new DeepCopyTest();
        People people = test.new People("Autism", 21, test.new Address("HeFei"));
        People clone = (People) people.clone();
        System.out.println(people.address == clone.address);
    }

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

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

        @Override
        protected Object clone() throws CloneNotSupportedException {
            People p = (People) super.clone(); // 先浅拷贝
            p.address = (Address) address.clone(); // 引用字段手动拷贝
            return p;
        }
    }
    class Address implements Cloneable{
        String city;
        public Address(String city){
            this.city = city;
        }
        @Override
        protected Object clone() throws CloneNotSupportedException {
            return super.clone();
        }
    }
}

• 序列化实现

public static Object deepCopy(Object object) {
    try {
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(bos);
        oos.writeObject(object);
        ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
        ObjectInputStream ois = new ObjectInputStream(bis);
        return ois.readObject();
    } catch (Exception e) {
        e.printStackTrace();
        return null;
    }
}