Java 浅克隆、深克隆

浅克隆

只复制了基本数据类型和String数据类型以及对应的数组类型，其他引用数据类型只是复制了引用地址；

使用方式

实现Cloneable接口，然后重写clone方法，调用super.clone()即可

public static class Person implements Cloneable {
    @Override
    protected Person clone() throws CloneNotSupportedException {
         return (Person) super.clone();
    }
}

例如

public static class Person implements Cloneable {
    public String name;
    public int age;
    public String[] names;
    public Baby baby;
    public ArrayList<String> names2 = new ArrayList<>();
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
    @Override
    public String toString() {
        return "Person{" + "name='" + name + '\'' + ", age=" + age + ", names=" + Arrays.toString(names) + ", baby=" + baby + ", names2=" + names2 + '}';
    }
    @Override
    protected Person clone() throws CloneNotSupportedException {
        return (Person) super.clone();
    }
}
public static class Baby implements Cloneable {
    public String name;
    public int age;
    public String[] names;
    public Baby(String name, int age, String[] names) {
        this.name = name;
        this.age = age;
        this.names = names;
    }
    @Override
    public String toString() {
        return "Baby{" + "name='" + name + '\'' + ", age=" + age + ", names=" + Arrays.toString(names) + '}';
    }
    @Override
    protected Baby clone() throws CloneNotSupportedException {
        return (Baby) super.clone();
    }
}
public static void main(String[] args) throws CloneNotSupportedException {
    Person person = new Person("person", 10);
    person.names = new String[]{"qq", "www"};
    person.baby = new Baby("baby", 20, new String[]{"qqqqq", "wwwww"});
    person.names2.add("1111");
    person.names2.add("2222");
    //  对克隆后的数据进行更改
    Person clone = person.clone();
    clone.name = "person1";
    clone.age = 23;
    clone.names2.add("3333");
    clone.names = new String[]{"111", "222"};

    clone.baby.name = "baby1";
    clone.baby.names = new String[]{"ttttt"};
    
    System.out.println(person.toString());
    System.out.println(clone.toString());
}

对应输出

Person{name='person', age=10, names=[qq, www], baby=Baby{name='baby1', age=20, names=[ttttt]}, names2=[1111, 2222, 3333]}
Person{name='person1', age=23, names=[111, 222], baby=Baby{name='baby1', age=20, names=[ttttt]}, names2=[1111, 2222, 3333]}

结论

发现，在对克隆的数据进行数据更改后：

• 基本数据类型，String，基本数据类型和String对应的数组，复制了一份，更改不会影响原始数据；
• 引用类型数据，只是复制了引用地址，对克隆后的引用数据类型操作，原始数据也会变，如测试中的Baby对象；

---

深克隆

对引用数据类型创建新的对象，并将属性克隆过去；需要递归克隆引用数据类型；

实现方式

public static class Person implements Cloneable {
    @Override
    protected Person clone() throws CloneNotSupportedException {
        Person person = (Person) super.clone();
        person.baby = baby.clone();
        person.names2 = (ArrayList<String>) names2.clone();
        return person;
    }
}

例如

将上面浅克隆的例子中的clone方法改成

public static class Person implements Cloneable {
    @Override
    protected Person clone() throws CloneNotSupportedException {
        Person person = (Person) super.clone();
        person.baby = baby.clone();
        person.names2 = (ArrayList<String>) names2.clone();
        return person;
    }
}

输出

Person{name='person', age=10, names=[qq, www], baby=Baby{name='baby', age=20, names=[qqqqq, wwwww]}, names2=[1111, 2222]}
Person{name='person1', age=23, names=[111, 222], baby=Baby{name='baby1', age=20, names=[ttttt]}, names2=[1111, 2222, 3333]}

结论

• 引用数据类型创建了一份新的数据，对克隆的数据更改，不会影响原始数据；

---

注意

1. 必须实现Cloneable接口，否则调用clone方法抛出异常

Object的clone方法的实现

protected Object clone() throws CloneNotSupportedException {
   if (!(this instanceof Cloneable)) {
       throw new CloneNotSupportedException("Class " + getClass().getName() +" doesn't implement Cloneable");
   }
   return internalClone();
}

 /*
 * Native helper method for cloning.
 */
@FastNative
private native Object internalClone();

2. 深克隆时子类也要复写clone方法

父类实现了clone方法，如果子类不覆写，那么子类只能浅克隆；

转载于:https://www.jianshu.com/p/afd772a2c6d0