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中对象的克隆是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)
说明下两个概念
1、 Clone和Copy
假设现在有一个Employee对象,Employee jack=new Employee("jack",5000),通常我们会有这样的赋值Employee tom=jack,这个时候只是简单了copy了一下reference,
tom和jack都指向内存中同一个object,这样tom或者jack的任何一个操作都可能影响到对方。打个比方,如果我们通过jack.raiseSalary()方法改变了salary域的值,那么tom
通过getSalary()方法得到的就是修改之后的salary域的值,显然这不是我们愿意看到的。我们希望得到jack的一个精确拷贝,同时两者互不影响,这时候我们就可以使用Clone
来满足我们的需求。Employee tom=jack.clone(),这时会生成一个新的Employee对象,并且和jack具有相同的属性值和方法。
2、 浅克隆和深克隆
Clone是如何完成的呢?Object在对某个对象实施Clone时对其是一无所知的,它仅仅是简单地执行域对域的copy,这就是浅克隆。现在问题来了,以Employee为例,它里
面有一个域hireDay不是基本型别的变量,而是一个reference变量,经过Clone之后就会产生一个新的Date型别的reference,它和原始对象中对应的域指向同一个Date对象,
这样克隆类就和原始类共享了一部分信息,而这样显然是不利的,过程下图所示:
这个时候我们就需要进行深克隆了,对那些非基本型别的域进行特殊的处理,例如本例中的hireDay。
浅复制(浅克隆)的例子如下:
package com.stone.CloneTest; public class ShallowClone { 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(); } }
2.深复制(深Clone)例子:
package com.stone.CloneTest; 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; } }
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
package com.stone.CloneTest; import java.io.ByteArrayInputStream; import java.io.ByteArrayOutputStream; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.io.Serializable; public class SerializationCloneTest { 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(); } }