关于Java的clone()

相关要点:

1.必须实现Cloneable接口，这个接口只是一个标识；如果不实现，调用了clone()，运行时会报CloneNotSupportedException

2.clone是Object的方法，标识为protected，子类必须重写，标识符可改为public

3.对于jdk1.5,clone可以返回相应类的类型或Object；对于1.4，只能返回Object

4.注意深复制和浅复制

 

 

浅复制

(1)对于int,double,Double,String等基本类型，super.clone()是采用的深复制

 

[java] view plain copy print ?

1. public class TestShallow implements Cloneable {  
2.     public int a;  
3.     public String b;  
4.     public Double c;  
5.     public TestShallow clone() throws CloneNotSupportedException{  
6.         return (TestShallow)super.clone();  
7.     }  
8. }  
9. class Test {  
10.     public static void main(String[] args) throws CloneNotSupportedException {  
11.         TestShallow a = new TestShallow();  
12.         a.a = 12;  
13.         a.b = "hahaa";  
14.         a.c = 14.11;  
15.         System.out.println("a原值");  
16.         print(a);  
17.         TestShallow b = a.clone();  
18.         b.a = 13;  
19.         b.b = "hahab";  
20.         b.c = 15.11;  
21.         System.out.println("a现值");  
22.         print(a);  
23.         System.out.println("b现值");  
24.         print(b);  
25.     }  
26.       
27.     public static void print(TestShallow a) {  
28.         System.out.println("a=" + a.a);  
29.         System.out.println("b=" + a.b);  
30.         System.out.println("c=" + a.c);  
31.     }  
32. }  

public class TestShallow implements Cloneable { public int a; public String b; public Double c; public TestShallow clone() throws CloneNotSupportedException{ return (TestShallow)super.clone(); } } class Test { public static void main(String[] args) throws CloneNotSupportedException { TestShallow a = new TestShallow(); a.a = 12; a.b = "hahaa"; a.c = 14.11; System.out.println("a原值"); print(a); TestShallow b = a.clone(); b.a = 13; b.b = "hahab"; b.c = 15.11; System.out.println("a现值"); print(a); System.out.println("b现值"); print(b); } public static void print(TestShallow a) { System.out.println("a=" + a.a); System.out.println("b=" + a.b); System.out.println("c=" + a.c); } }  

结果:

a原值
a=12
b=hahaa
c=14.11
a现值
a=12
b=hahaa
c=14.11
b现值
a=13
b=hahab
c=15.11

(2)对其他类及自定义类，默认采用的是浅复制

[java] view plain copy print ?

1. class A {  
2.     public String a;  
3. }  
4. public class TestShallow1 implements Cloneable {  
5.     public int a;  
6.     public A b;  
7.     public TestShallow1() {  
8.         b = new A();  
9.     }  
10.     public TestShallow1 clone() throws CloneNotSupportedException{  
11.         return (TestShallow1)super.clone();  
12.     }  
13. }  
14. class Test1 {  
15.     public static void main(String[] args) throws CloneNotSupportedException {  
16.         TestShallow1 a = new TestShallow1();  
17.         a.a = 12;  
18.         a.b.a = "hahaa";  
19.         System.out.println("a原值");  
20.         print(a);  
21.         TestShallow1 b = a.clone();  
22.         b.a = 13;  
23.         b.b.a = "hahab";  
24.         System.out.println("a现值");  
25.         print(a);  
26.         System.out.println("b现值");  
27.         print(b);  
28.     }  
29.       
30.     public static void print(TestShallow1 a) {  
31.         System.out.println("a=" + a.a);  
32.         System.out.println("b=" + a.b.a);  
33.     }  
34. }  

class A { public String a; } public class TestShallow1 implements Cloneable { public int a; public A b; public TestShallow1() { b = new A(); } public TestShallow1 clone() throws CloneNotSupportedException{ return (TestShallow1)super.clone(); } } class Test1 { public static void main(String[] args) throws CloneNotSupportedException { TestShallow1 a = new TestShallow1(); a.a = 12; a.b.a = "hahaa"; System.out.println("a原值"); print(a); TestShallow1 b = a.clone(); b.a = 13; b.b.a = "hahab"; System.out.println("a现值"); print(a); System.out.println("b现值"); print(b); } public static void print(TestShallow1 a) { System.out.println("a=" + a.a); System.out.println("b=" + a.b.a); } }

结果：

a原值
a=12
b=hahaa
a现值
a=12
b=hahab
b现值
a=13
b=hahab

 

深复制

对于其中非基本类型的字段，必须明确进行其赋值

[java] view plain copy print ?

1. class A implements Cloneable {  
2.     public String a;  
3.     public A clone() throws CloneNotSupportedException{  
4.         return (A)super.clone();  
5.     }  
6. }  
7. public class TestDeep implements Cloneable {  
8.     public int a;  
9.     public A b;  
10.     public TestDeep() {  
11.         b = new A();  
12.     }  
13.     public TestDeep clone() throws CloneNotSupportedException{  
14.         TestDeep clone = (TestDeep)super.clone();  
15.         clone.b = this.b.clone();  
16.         return clone;  
17.     }  
18. }  
19. class Test1 {  
20.     public static void main(String[] args) throws CloneNotSupportedException {  
21.         TestDeep a = new TestDeep();  
22.         a.a = 12;  
23.         a.b.a = "hahaa";  
24.         System.out.println("a原值");  
25.         print(a);  
26.         TestDeep b = a.clone();  
27.         b.a = 13;  
28.         b.b.a = "hahab";  
29.         System.out.println("a现值");  
30.         print(a);  
31.         System.out.println("b现值");  
32.         print(b);  
33.     }  
34.       
35.     public static void print(TestDeep a) {  
36.         System.out.println("a=" + a.a);  
37.         System.out.println("b=" + a.b.a);  
38.     }  
39. }  

class A implements Cloneable { public String a; public A clone() throws CloneNotSupportedException{ return (A)super.clone(); } } public class TestDeep implements Cloneable { public int a; public A b; public TestDeep() { b = new A(); } public TestDeep clone() throws CloneNotSupportedException{ TestDeep clone = (TestDeep)super.clone(); clone.b = this.b.clone(); return clone; } } class Test1 { public static void main(String[] args) throws CloneNotSupportedException { TestDeep a = new TestDeep(); a.a = 12; a.b.a = "hahaa"; System.out.println("a原值"); print(a); TestDeep b = a.clone(); b.a = 13; b.b.a = "hahab"; System.out.println("a现值"); print(a); System.out.println("b现值"); print(b); } public static void print(TestDeep a) { System.out.println("a=" + a.a); System.out.println("b=" + a.b.a); } }

结果:

a原值
a=12
b=hahaa
a现值
a=12
b=hahaa
b现值
a=13
b=hahab