java对象拷贝

JAVA 对象拷贝

JAVA 对象拷贝

为什么需要有对象拷贝？

对象拷贝相对的自然是引用拷贝。java初学者经常会问，我这个方法要改变一个对象的属性，可以把参数传进去了，为什么没有改变了？

——基本数据类型传值，而对象传引用或引用的拷贝。

而有时候我们要获取到一个当前状态的对象复制品，他们是两个独立对象。不再是引用或者引用拷贝（实质都是指向对象本身）。就是说a是b的拷贝，b发生变化的时候，不要影响a。

对象拷贝有浅拷贝和深度拷贝两种。

1）浅拷贝

浅拷贝是指对象中基本数据类型得到拷贝，而引用数据类型并未拷贝。
提到拷贝自然和clone联系起来了，所有具有clone功能的类都有一个特性，那就是它直接或间接地实现了Cloneable接口。
否则，我们在尝试调用clone（）方法时，将会触发CloneNotSupportedException异常。
eg:

1 public class DOG implements Cloneable
2 {
3 public DOG(String name, int age)
4 {
5 this .name = name;
6 this .age = age;
7 }
8
9 public String getName()
10 {
11 return this .name;
12 }
13
14 public int getAge()
15 {
16 return this .age;
17 }
18
19 public Object clone()
20 {
21 try
22 {
23 return super .clone();
24
25 } catch (CloneNotSupportedException e)
26 {
27 return null ;
28 }
29 }
30
31 public String name;
32
33 private int age;
34
35 // test
36 public static void main(String[] args)
37 {
38 DOG dog1 = new DOG( " xiaogou " , 2 );
39 DOG dog2 = (DOG) dog1.clone();
40 dog1.name = " dagou " ;
41 System.out.println(dog2.getName());
42 System.out.println(dog2.getAge());
43 System.out.println(dog1.getName());
44 System.out.println(dog1.getAge());
45
46 }
47
48 }
49

运行结果：

xiaogou
2
dagou
2

2）深度拷贝

相对浅拷贝。实现对象中基本数据类型和引用数据类型的拷贝。

请先看下面代码：

1 class AAA
2 {
3 public AAA(String name)
4 {
5 this .name = name;
6 }
7
8 public String name;
9 }
10
11 class DOG implements Cloneable
12 {
13 public DOG(String name, int age, AAA birthday)
14 {
15 this .name = name;
16 this .age = age;
17 this .birthday = birthday;
18 }
19
20 public String getName()
21 {
22 return name;
23 }
24
25 public int getAge()
26 {
27 return age;
28 }
29
30 public AAA getBirthday()
31 {
32 return birthday;
33 }
34
35 public String getBirth(AAA a)
36 {
37 return a.name;
38 }
39
40 public String name;
41
42 private int age;
43
44 public AAA birthday;
45
46 public Object clone()
47 {
48 try
49 {
50 super .clone();
51 return super .clone();
52 } catch (Exception e)
53 {
54 return null ;
55 }
56 }
57 }
58
59 public class TestClone
60 {
61 public static void main(String[] args)
62 {
63 AAA Day = new AAA( " test " );
64 DOG dog1 = new DOG( " xiaogou " , 2 , Day);
65 DOG dog2 = (DOG) dog1.clone();
66 // dog2.birthday = (AAA) dog1.birthday.clone();
67 dog1.birthday.name = " 333 " ;
68 System.out.println(dog1.getBirth(dog1.birthday));
69 System.out.println(dog2.getBirth(dog2.birthday));
70 }
71 }
72

运行结果是：
333
333
而真正要实现拷贝还的加点代码，如下请对比上面和下面代码的异同之处：

1 class AAA implements Cloneable
2 {
3 public AAA(String name)
4 {
5 this .name = name;
6 }
7
8 public Object clone()
9 {
10 try
11 {
12 super .clone();
13 return super .clone();
14 } catch (Exception e)
15 {
16 return null ;
17 }
18 }
19
20 public String name;
21 }
22
23 class DOG implements Cloneable
24 {
25 public DOG(String name, int age, AAA birthday)
26 {
27 this .name = name;
28 this .age = age;
29 this .birthday = birthday;
30 }
31
32 public String getName()
33 {
34 return name;
35 }
36
37 public int getAge()
38 {
39 return age;
40 }
41
42 public AAA getBirthday()
43 {
44 return birthday;
45 }
46
47 public String getBirth(AAA a)
48 {
49 return a.name;
50 }
51
52 public String name;
53
54 private int age;
55
56 public AAA birthday;
57
58 public Object clone()
59 {
60 try
61 {
62 super .clone();
63 return super .clone();
64 } catch (Exception e)
65 {
66 return null ;
67 }
68 }
69 }
70
71 public class TestClone
72 {
73 public static void main(String[] args)
74 {
75 AAA Day = new AAA( " test " );
76 DOG dog1 = new DOG( " xiaogou " , 2 , Day);
77 DOG dog2 = (DOG) dog1.clone();
78 dog2.birthday = (AAA) dog1.birthday.clone(); // 特别注意这里
79 dog1.birthday.name = " 333 " ;
80 System.out.println(dog1.getBirth(dog1.birthday));
81 System.out.println(dog2.getBirth(dog2.birthday));
82 }
83 }
84

运行结果：
333
test
这样基本就达到了我们当初的母的。

但是明显的这种方法还是有许多不足，人们总是希望一个clone就是对象直接克隆。而上面还要对对象中的对象递归使用clone。下面提供一种更高级点的做法：

1 import java.io. * ;
2
3 class AAA implements Serializable
4 {
5 public AAA(String name)
6 {
7 this .name = name;
8 }
9
10 public String name;
11 }
12
13 class DOG extends SerialCloneable
14 {
15 public DOG(String name, int age, AAA birthday)
16 {
17 this .name = name;
18 this .age = age;
19 this .birthday = birthday;
20 }
21
22 public String getName()
23 {
24 return name;
25 }
26
27 public int getAge()
28 {
29 return age;
30 }
31
32 public AAA getBirthday()
33 {
34 return birthday;
35 }
36
37 public String getBirth(AAA a)
38 {
39 return a.name;
40 }
41
42 public String name;
43
44 private int age;
45
46 public AAA birthday;
47
48 public Object clone()
49 {
50 try
51 {
52 super .clone();
53 return super .clone();
54 } catch (Exception e)
55 {
56 return null ;
57 }
58 }
59 }
60
61 public class TestClone
62 {
63 public static void main(String[] args)
64 {
65 AAA Day = new AAA( " test " );
66 DOG dog1 = new DOG( " xiaogou " , 2 , Day);
67 DOG dog2 = (DOG) dog1.clone();
68 // dog2.birthday = (AAA) dog1.birthday.clone();
69 dog1.birthday.name = " 333 " ;
70 System.out.println(dog1.getBirth(dog1.birthday));
71 System.out.println(dog2.getBirth(dog2.birthday));
72 }
73 }
74
75 class SerialCloneable implements Cloneable, Serializable
76 {
77 public Object clone()
78 {
79 try
80 {
81 ByteArrayOutputStream bout = new ByteArrayOutputStream();
82 ObjectOutputStream out = new ObjectOutputStream(bout);
83 out.writeObject( this );
84 out.close();
85 ByteArrayInputStream bin = new ByteArrayInputStream(bout
86 .toByteArray());
87 ObjectInputStream in = new ObjectInputStream(bin);
88 Object ret = in.readObject();
89 in.close();
90 return ret;
91 } catch (Exception e)
92 {
93 return null ;
94 }
95 }
96 }
97

输出：
333
test

上面的代码用序列化与反序列化实现了对象拷贝。比较通用。但是得注意的是其中的类得implements Serializable。