关于Java的clone()

最新推荐文章于 2024-06-04 00:08:04 发布

gtuu0123

最新推荐文章于 2024-06-04 00:08:04 发布

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分类专栏： Java相关文章标签： java string class object jdk c

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本文探讨了Java中实现Cloneable接口与使用clone方法的基本原理。通过实例演示了浅复制与深复制的区别，展示了如何正确地进行对象复制，避免引用共享导致的问题。

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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

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

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

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