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想要复制一个对象的所有属性，简单的方式就是通过Cloneable接口，你还可以使用工具类BeanUtils的copyProperties方法，还可以使用拷贝工厂或者使用序列化。这篇文章主要介绍怎么使用Cloneable来完成对象的拷贝。
Cloneable接口的作用是表明这个对象允许克隆。如果一个类实现了Cloneable，那么Object的clone方法就返回该对象的逐域拷贝；没有实现Cloneable，调用Object的clone方法将会抛出CloneNotSupportedException异常。一个简单的例子
@Data@Builder@NoArgsConstructor@AllArgsConstructorpublic class People implements Cloneable { private Long id; private String code; private String name; private Integer age; @Override public People clone() { People people; try { people = (People) super.clone(); } catch (CloneNotSupportedException e) { e.printStackTrace(); throw new AssertionError();//can't happen } return people; } public static void main(String[] args) { People.PeopleBuilder builder = People.builder(); People people = builder.id(12L) .name("mbtlami") .code("2018") .age(100) .build(); People clone = people.clone();//it's the clone object System.out.println(people); }} 但是如果对象的域中包含有可变的对象，使用以上方式只能简单的将可变对象的引用地址复制给克隆出来的对象。这样不管是原对象还是克隆对象，有一方修改了这个可变对象内的属性值，另一方同样会体现出来，这就导致了严重的后果。
在Person类中新增加一个引用对象“宠物”，修改people的宠物名称为cat，clone出来的对象的宠物名称也变为了cat：
private Pet pet;@Datapublic class Pet{ private String name;}public static void main(String[] args) { Pet dog = new Pet("dog"); People.PeopleBuilder builder = People.builder(); People people = builder.id(12L) .name("mbtlami") .code("2018") .age(100) .pet(dog) .build(); People clone = people.clone();//it's the clone object System.out.println(people); people.getPet().setName("cat");//modify Pet name System.out.println(clone);//print cat} 如何保证clone方法正常工作呢？必须进行深克隆。有一个需要注意的地方：clone和引用可变对象的final域是不兼容的，给Pet属性增加final修饰符将不能正常工作。
浅克隆(ShallowClone)和深克隆(DeepClone)都是克隆对象，他们的主要区别在于是否支持引用类型的成员变量的复制。那么怎么进行深克隆呢？让Pet实现Cloneable并重写clone方法，还需要修改People的clone方法。
@Datapublic class Pet implements Cloneable { private String name; public Pet(String name) { this.name = name; } @Override public Pet clone() { try { return (Pet) super.clone(); } catch (CloneNotSupportedException e) { e.printStackTrace(); throw new AssertionError(); } }}class People {... @Override public People clone() { People people; try { people = (People) super.clone(); if (pet != null) { people.pet = pet.clone(); } } catch (CloneNotSupportedException e) { e.printStackTrace(); throw new AssertionError();//can't happen } return people; }}people.getPet().setName("cat");System.out.println(clone);//People{id=12, code='2018', name='mbtlami', age=25, isMarried=null, pet=Pet(name=dog)} 如果People内定义了一个散列桶数组，实现了轻量级的单向链表，仅仅只是递归克隆对象，虽然被克隆的对象有它自己的散列桶，但是数组引用的链表还是和原对象一样的，这样也会导致问题。
class Person{... private Node [] table; static class Node { final int hash; final K key; V value; Node next; Node(int hash, K key, V value, Node next) { this.hash = hash; this.key = key; this.value = value; this.next = next; } ... } @Override public People clone() { People people; try { people = (People) super.clone(); if (pet != null) { people.pet = pet.clone(); } if (table != null) { people.table = table.clone(); } } catch (CloneNotSupportedException e) { e.printStackTrace(); throw new AssertionError();//can't happen } return people; }}