Java Object 对象拷贝
@author ixenos
JAVA 对象拷贝
Java里的clone分为：
1.浅拷贝：浅复制仅仅复制所考虑的对象，而不复制它所引用的对象，Object类里的clone方法是浅拷贝
2.深拷贝：深复制把要复制的对象及其所引用的对象都复制了一遍
3.序列化深拷贝：把对象写到流里的过程是序列化（Serilization）过程，而把对象从流中读出来的过程则叫做反序列化（Deserialization）过程。应当指出的是，写在流里的是对象的一个拷贝，而原对象仍然存在于JVM里面，利用这个特性，可以做深拷贝
深拷贝时必须要遵循下面三点：
1.在派生类中覆盖基类的clone()方法，并声明为public（Object类中的clone()方法为protected的）
2.在派生类的clone()方法中，调用super.clone()
3.在派生类中实现Cloneable接口
示例
浅拷贝的例子：
public class CloneTest
{ public static void main(String[] args) throws Exception
{
// teacher对象将被clone出来的Student对象共享.
Teacher teacher = new Teacher();
teacher.setAge(40);
teacher.setName("Teacher zhang"); Student student1 = new Student();
student1.setAge(20);
student1.setName("zhangsan");
student1.setTeacher(teacher); // 复制出来一个对象student2
Student student2 = (Student) student1.clone();
System.out.println(student2.getAge());
System.out.println(student2.getName()); System.out.println("~~~~~~~~~~~~~~~~~~~~~~");
System.out.println(student1.getTeacher().getAge());
System.out.println(student1.getTeacher().getName()); // 修改student2的引用对象
student2.getTeacher().setAge(50);
student2.getTeacher().setName("Teacher Li"); System.out.println("~~~~~~~~~~~~~~~~~~~~~~");
System.out.println(student1.getTeacher().getAge());
System.out.println(student1.getTeacher().getName());
}
} class Teacher
{
public int age;
public String name; public int getAge()
{
return age;
} public void setAge(int age)
{
this.age = age;
} public String getName()
{
return name;
} public void setName(String name)
{
this.name = name;
} } class Student implements Cloneable
{ public int age;
public String name;
public Teacher teacher; public int getAge()
{
return age;
} public void setAge(int age)
{
this.age = age;
} public String getName()
{
return name;
} public void setName(String name)
{
this.name = name;
} public Teacher getTeacher()
{
return teacher;
} public void setTeacher(Teacher teacher)
{
this.teacher = teacher;
} @Override
public Object clone() throws CloneNotSupportedException
{
return super.clone();
}
}
输出结果为：
20
zhangsan
~~~~~~~~~~~~~~~~~~~~~~
40
Teacher zhang
~~~~~~~~~~~~~~~~~~~~~~
50
Teacher Li
深拷贝例子：
public class DeepCloneTest
{ public static void main(String[] args) throws Exception
{
// teacher对象将不被clone出来的Student对象共享.
Teacher teacher = new Teacher();
teacher.setAge(40);
teacher.setName("Teacher zhang"); Student student1 = new Student();
student1.setAge(20);
student1.setName("zhangsan");
student1.setTeacher(teacher); // 复制出来一个对象student2
Student student2 = (Student) student1.clone();
System.out.println(student2.getAge());
System.out.println(student2.getName()); System.out.println("~~~~~~~~~~~~~~~~~~~~~~");
System.out.println(student1.getTeacher().getAge());
System.out.println(student1.getTeacher().getName()); // 修改student2的引用对象
student2.getTeacher().setAge(50);
student2.getTeacher().setName("Teacher Li"); System.out.println("~~~~~~~~~~~~~~~~~~~~~~");
System.out.println(student1.getTeacher().getAge());
System.out.println(student1.getTeacher().getName());
}
} class Teacher implements Cloneable
{
public int age;
public String name; public int getAge()
{
return age;
} public void setAge(int age)
{
this.age = age;
} public String getName()
{
return name;
} public void setName(String name)
{
this.name = name;
} @Override
public Object clone() throws CloneNotSupportedException
{
return super.clone();
} } class Student implements Cloneable
{ public int age;
public String name;
public Teacher teacher; public int getAge()
{
return age;
} public void setAge(int age)
{
this.age = age;
} public String getName()
{
return name;
} public void setName(String name)
{
this.name = name;
} public Teacher getTeacher()
{
return teacher;
} public void setTeacher(Teacher teacher)
{
this.teacher = teacher;
} @Override
public Object clone() throws CloneNotSupportedException
{
Student student = (Student) super.clone();
// 将引用的对象teacher也clone下
student.setTeacher((Teacher) (student.getTeacher().clone())); // student.getTeacher().clone()
return student;
}
} 输出结果为：
20
zhangsan
~~~~~~~~~~~~~~~~~~~~~~
40
Teacher zhang
~~~~~~~~~~~~~~~~~~~~~~
40
Teacher zhang
序列化深拷贝例子：
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
//利用序列化来做深复制
//深clone public class DeepCloneTest
{ public static void main(String[] args) throws Exception
{
// teacher对象将不被clone出来的Student对象共享.
Teacher teacher = new Teacher();
teacher.setAge(40);
teacher.setName("Teacher zhang"); Student student1 = new Student();
student1.setAge(20);
student1.setName("zhangsan");
student1.setTeacher(teacher); // 复制出来一个对象student2
Student student2 = (Student) student1.deepCopy();
System.out.println(student2.getAge());
System.out.println(student2.getName()); System.out.println("~~~~~~~~~~~~~~~~~~~~~~");
System.out.println(student1.getTeacher().getAge());
System.out.println(student1.getTeacher().getName()); // 修改student2的引用对象
student2.getTeacher().setAge(50);
student2.getTeacher().setName("Teacher Li"); System.out.println("~~~~~~~~~~~~~~~~~~~~~~");
System.out.println(student1.getTeacher().getAge());
System.out.println(student1.getTeacher().getName());
}
} class Teacher implements Serializable
{ private static final long serialVersionUID = -8834559347461591191L; public int age;
public String name; public int getAge()
{
return age;
} public void setAge(int age)
{
this.age = age;
} public String getName()
{
return name;
} public void setName(String name)
{
this.name = name;
} } class Student implements Serializable
{ // serialVersionUID
// 如果你的对象序列化后存到硬盘上面后，可是后来你却更改了类的field(增加或减少或改名)，当你反序列化时，就会出现Exception的，这样就会造成不兼容性的问题。
// 但当serialVersionUID相同时，它就会将不一样的field以type的缺省值赋值(如int型的是0,String型的是null等)，这个可以避开不兼容性的问题。所以最好给serialVersionUID赋值
private static final long serialVersionUID = 7991552226614088458L; public int age;
public String name;
public Teacher teacher;
public int getAge()
{
return age;
}
public void setAge(int age)
{
this.age = age;
}
public String getName()
{
return name;
}
public void setName(String name)
{
this.name = name;
} public Teacher getTeacher()
{
return teacher;
} public void setTeacher(Teacher teacher)
{
this.teacher = teacher;
}
/**
* 因为对象序列化会自然地对对象深拷贝，再利用“序列化-反序列化”读出
*/
public Object deepCopy() throws Exception
{
// 将该对象序列化成流,因为写在流里的是对象的一个拷贝，而原对象仍然存在于JVM里面。所以利用这个特性可以实现对象的深拷贝
ByteArrayOutputStream bos = new ByteArrayOutputStream(); ObjectOutputStream oos = new ObjectOutputStream(bos);
//this很关键，引用当前对象，当然，这是值传递
oos.writeObject(this); // 将流序列化成对象
ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray()); ObjectInputStream ois = new ObjectInputStream(bis); return ois.readObject();
}
} 输出结果为：
20
zhangsan
~~~~~~~~~~~~~~~~~~~~~~
40
Teacher zhang
~~~~~~~~~~~~~~~~~~~~~~
40
Teacher zhang