java深浅复制

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一、概念
二、实现方式及简单原理
三、实例
四、参考
五、单元测试
 六、代码下载（deepCopy.rar）

一、概念

A、浅复制：浅复制仅仅复制所考虑的对象，而不复制它所引用的对象

被复制对象的所有变量都含有与原来的对象相同的值，而所有的对其他对象的引用仍然指向原来的对象。

B、深复制：深复制把要复制的对象所引用的对象都复制了一遍

被复制对象的所有变量都含有与原来的对象相同的值，除去那些引用其他对象的变量。那些引用其他对象的变量将指向被复制过的新对象，而不再是原有的那些被引用的对象。

二、实现方式及原理

1、浅复制：实现Cloneable接口，重写clone()方法（）

2、深复制：实现serializable接口，字节流转化为对象流来处理

三、实例

A、浅复制

public class Student implements Cloneable {

public String studentName;

public int studentAge;

public Student(String studentName, int studentAge) {

this.studentName = studentName;

this.studentAge = studentAge;

}

@Override

public Student clone() throws CloneNotSupportedException {

return (Student)super.clone();

}

B1、深复制（Cloneable） B2、深复制（Serializable）

public class Teacher implements Cloneable,Serializable {

String teacherName;

int teacherAge;

public Teacher(String teacherName, int teacherAge) {

this.teacherName = teacherName;

this.teacherAge = teacherAge;

}

@Override

protected Object clone() throws CloneNotSupportedException {

return super.clone();

}

public class Man implements Cloneable,Serializable {

String name;

int age;

public Teacher teacher;

public Man(String name, int age, Teacher teacher) {

this.name = name;

this.age = age;

this.teacher = teacher;

}

@Override

public Object clone() throws CloneNotSupportedException {

Man man = null;

man = (Man)super.clone();

man.teacher = (Teacher) teacher.clone(); //important

return man;

}

/**

* serialized copy

* @return Man

* @throws IOException

* @throws ClassNotFoundException

public Object serialClone() throws IOException, ClassNotFoundException {

ByteArrayOutputStream baos = new ByteArrayOutputStream();

ObjectOutputStream oos = new ObjectOutputStream(baos);

oos.writeObject(this);

ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());

ObjectInputStream ois = new ObjectInputStream(bais);

return ois.readObject();

}

四、参考：

（经典）http://blog.csdn.net/guitacom/article/details/665055#

http://dev.firnow.com/course/3_program/java/javashl/2008510/115047.html

五、单元测试代码

public class StudentTest {

@BeforeClass

public static void setUpBeforeClass() throws Exception {

}

@Test

public void testShallowClone() throws Exception {

String name = "Robert C. Martin";

int age = 40;

Student student = new Student(name, age);

Student studentCopy = (Student) student.clone();

studentCopy.studentName = "Kent Benk";

studentCopy.studentAge = 55;

assertEquals(student.studentName, "Robert C. Martin");

assertEquals(student.studentAge, 40);

}

@Test

public void testDeepClone() throws CloneNotSupportedException {

String manName = "Robert C. Martin";

int manAge = 40;

String teacherName = "T1";

int teacherAge = 50;

Teacher teacher = new Teacher(teacherName, teacherAge);

Man man = new Man(manName, manAge, teacher);

Man replication = (Man)man.clone();

replication.teacher.teacherName = "T2";

replication.teacher.teacherAge = 60;

assertEquals(man.teacher.teacherName, "T1"); //original teacher's properties don't change

assertEquals(man.teacher.teacherAge, 50);

}

@Test

public void testSerialDeepClone() throws IOException, ClassNotFoundException {

String manName = "Robert C. Martin";

int manAge = 40;

int teacherAge = 50;

String teacherName = "T1";

Teacher teacher = new Teacher(teacherName, teacherAge);

Man man = new Man(manName, manAge, teacher);

Man replication = (Man) man.serialClone();

replication.teacher.teacherName = "T2";

replication.teacher.teacherAge = 60;

assertEquals(man.teacher.teacherName, "T1"); //original teacher's properties don't change

assertEquals(man.teacher.teacherAge, 50);

}

posted on 2012-04-13 14:47 zhb8015 阅读(657) 评论(1) 编辑收藏所属分类: interview

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# re: java深浅复制 回复 更多评论

补充一下：
七、性能测试：
测试结果：复制100000 克隆复制是串行化复制的74倍
100000 clone time:47
100000 serial clone time:3500
Multiple is(serial/clone):74

测试单元的代码：
******************
@Test
public void deepCloneVsSerial() throws CloneNotSupportedException, IOException, ClassNotFoundException {
int max = 100000;

String manName = "Robert C. Martin";
int manAge = 40;

int teacherAge = 50;
String teacherName = "T1";
Teacher teacher = new Teacher(teacherName, teacherAge);

Man man = new Man(manName, manAge, teacher);

//begin
long start1 = System.currentTimeMillis();
for (int i = 0; i < max; i++) {
man.clone();
}
long end1 = System.currentTimeMillis();
System.err.println(max + " clone time:" + (end1 - start1));

long start2 = System.currentTimeMillis();
for (int i = 0; i < max; i++) {
man.serialClone();
}
long end2 = System.currentTimeMillis();
System.err.println(max + " serial clone time:" + (end2 - start2));

System.err.println("Multiple is(serial/clone):" + (end2 - start2)/(end1 - start1));
/**
* 100000 clone time:47
100000 serial clone time:3438
Multiple is(serial/clone):73
*/
}

******************

2012-04-13 15:24 | zhb8015

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