JAVA-Clone 对象拷贝

JAVA 中对象的赋值是复制对象的引用，即复制引用

public static void main(String[] args) {
    User user = new User(1,"asds",18);
    User user1 = user;

    System.out.println(user);
    System.out.println(user1);
}

JAVA 中复制对象(克隆副本，互不影响)

使用 clone() 方法要求被克隆对象实现 Cloneable 接口，修改覆盖的 clone() 方法的修饰符为 public

public class User implements Cloneable {
    private Integer id;
    private String name;
    private Integer age;

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

再测试

public static void main(String[] args) throws CloneNotSupportedException {
    User user = new User(1,"asds",18);
    User user1 = (User) user.clone();

    System.out.println(user);
    System.out.println(user1);
}

浅拷贝

public class Address {
    private String address;

public class User implements Cloneable {
    private Integer id;
    private String name;
    private Integer age;
    private Address address;

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

测试

public static void main(String[] args) throws CloneNotSupportedException {
    Address address = new Address("wuhan");
    User user = new User(1,"asds",18,address);
    User user1 = (User) user.clone();

    // System.identityHashCode() 获取对象唯一标识，若对象不重写 hashCode() 则值和 Object.hashCode() 一样
    System.out.println(System.identityHashCode(user)+"\t"+user);
    System.out.println(System.identityHashCode(user1)+"\t"+user1);

    user.getAddress().setAddress("beijing");

    System.out.println(user.hashCode()+"\t"+user);
    System.out.println(user1.hashCode()+"\t"+user1);
}

只修改 user，但 user1 也被修改

clone() 方法：属性为基本类型拷贝其值，属性为非基本类型拷贝其引用

深拷贝

public class Address implements Cloneable {
    private String address;

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

public class User implements Cloneable {
    private Integer id;
    private String name;
    private Integer age;
    private Address address;

    @Override
    public Object clone() throws CloneNotSupportedException {
        Object clone = super.clone();
        Object addressClone = ((User) clone).getAddress().clone();
        ((User) clone).setAddress((Address) addressClone);
        return clone;
    }

再测试

实现完整的深拷贝，需要被复制对象的继承链、引用链上的每一个对象都实现克隆机制

被克隆的对象的属性都是基本类型，那只需要被克隆类实现 cloneable 接口即可，若对象的属性包含其他非基本类型对象，那么这些非基本类型的对象都需要实现 cloneable 接口

对象属性少这样做还可以完成深拷贝，如果有多个对象属性，多层引用关系，就会比较棘手，这时候可用JAVA的序列化机制来完成对象的深拷贝

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https://blog.csdn.net/54powerman/article/details/64920431