1.java里的clone分为:
A:浅复制(浅克隆): 浅复制仅仅复制所考虑的对象,而不复制它所引用的对象。
b:深复制(深克隆):深复制把要复制的对象所引用的对象都复制了一遍。
Java中对象的克隆,为了获取对象的一份拷贝,我们可以利用Object类的clone()方法。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。
Object类里的clone方法是浅复制(浅克隆)
浅复制(浅克隆)的例子如下:
- 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
2.深复制(深Clone)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()));
- return student;
- }
- }
- 输出结果为:
- 20
- zhangsan
- ~~~~~~~~~~~~~~~~~~~~~~
- 40
- Teacher zhang
- ~~~~~~~~~~~~~~~~~~~~~~
- 40
- Teacher zhang
3.利用序列化来做深复制,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
。
- 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;
- }
- 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);
- 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