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
public class DOG implements Cloneable2
{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
class AAA2
{3
public AAA(String name)4
{5
this .name = name;6
} 7
8
public String name;9
} 10
11
class DOG implements Cloneable12
{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 TestClone60
{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
class AAA implements Cloneable2
{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 Cloneable24
{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 TestClone72
{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
import java.io. * ;2
3
class AAA implements Serializable4
{5
public AAA(String name)6
{7
this .name = name;8
} 9
10
public String name;11
} 12
13
class DOG extends SerialCloneable14
{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 TestClone62
{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, Serializable76
{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(bout86
.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。
3）后记
我们如果利用强大的反射机制+序列化与反序列化，能做出更加灵活的对象拷贝。有兴趣的朋友可以自行去研究。
我在javaeye上看到一篇短文：http://www.javaeye.com/post/367014 主要讲的就是反射在对象拷贝中的应用。
