Cloneable接口
1、Cloneable接口
Cloneable是一个接口，实现这个接口后，可以在类中重写Object中的clone方法，然后通过类调用clone方法进行克隆，如果不实现Cloneable接口，则会抛出CloneNotSupportedException异常。Object中clone方法：
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| protected native Object clone() throws CloneNotSupportedException
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2、Object中的clone方法是一个空的方法，那么他是如何判断类是否实现了Cloneable接口呢？
原因在于这个方法中有一个native关键字修饰。
native修饰的方法都是空的方法，但是这些方法都是有实现体的（这里也就间接说明了native关键字不能与abstract同时使用。因为abstract修饰的方法与java的接口中的方法类似，他显式的说明了修饰的方法，在当前是没有实现体的，abstract的方法的实现体都由子类重写），只不过native方法调用的实现体，都是非java代码编写的（例如：调用的是在jvm中编写的C的接口），每一个native方法在jvm中都有一个同名的实现体，native方法在逻辑上的判断都是由实现体实现的，另外这种native修饰的方法对返回类型，异常控制等都没有约束。
由此可见，这里判断是否实现cloneable接口，是在调用jvm中的实现体时进行判断的。
3、为什么要克隆？
clone方法克隆的对象包含已经修改过的属性，而new出来的对象是一个新的对象，对应的属性没有值。所以我们还要重新给这个对象赋值。所以当需要一个新的对象来保存当前对象的状态时可以使用clone方法。
4、如何实现克隆？
- 对象的类实现
Cloneable接口。
- 覆盖
Object类的clone()方法 。
- 在
clone()方法中调用super.clone()。
5、浅克隆(ShallowClone)和深克隆(DeepClone)
5.1 浅克隆
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| public class Student implements Cloneable {
private String name;
private int age;
private StringBuffer sex;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public StringBuffer getSex() {
return sex;
}
public void setSex(StringBuffer sex) {
this.sex = sex;
}
@Override
public String toString() {
return "Student{" +
"name='" + name + '\'' +
", age=" + age +
", sex=" + sex +
'}';
}
}
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public class School implements Cloneable{
private String schoolName;
private int stuNums;
private Student stu;
public String getSchoolName() {
return schoolName;
}
public void setSchoolName(String schoolName) {
this.schoolName = schoolName;
}
public int getStuNums() {
return stuNums;
}
public void setStuNums(int stuNums) {
this.stuNums = stuNums;
}
public Student getStu() {
return stu;
}
public void setStu(Student stu) {
this.stu = stu;
}
@Override
protected Object clone() throws CloneNotSupportedException {
return super.clone();
}
@Override
public String toString() {
return "School{" +
"schoolName='" + schoolName + '\'' +
", stuNums=" + stuNums +
", stu=" + stu +
'}';
}
@Test
public void test1() throws CloneNotSupportedException {
School s1 = new School();
s1.setSchoolName("实验小学");
s1.setStuNums(100);
Student stu1 = new Student();
stu1.setAge(20);
stu1.setName("zhangsan");
stu1.setSex(new StringBuffer("男"));
s1.setStu(stu1);
System.out.println("s1: "+s1+"\ns1的hashcode:"+s1.hashCode()+" s1中schoolName的hashcode:"+s1.getSchoolName().hashCode()+" s1中stu1的hashcode:"+s1.getStu().hashCode());
School s2 = (School)s1.clone();
System.out.println("s2: "+s2+"\ns2的hashcode:"+s2.hashCode()+" s2中schoolName的hashcode:"+s2.getSchoolName().hashCode()+" s2中stu1的hashcode:"+s2.getStu().hashCode());
}
}
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| s1: School{schoolName='实验小学', stuNums=100, stu=Student{name='zhangsan', age=20, sex=男}}
s1的hashcode:1535128843 s1中schoolName的hashcode:737493093 s1中stu1的hashcode:1567581361
s2: School{schoolName='实验小学', stuNums=100, stu=Student{name='zhangsan', age=20, sex=男}}
s2的hashcode:849460928 s2中schoolName的hashcode:737493093 s2中stu1的hashcode:1567581361
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s1的hashcode不等于s2的hashcode
s1中schoolName的hashcode等于s2中schoolName的hashcode
s1中stu1的hashcode等于s2中stu1的hashcode
5.2 深克隆
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| package dao;
import org.junit.Test;
public class School implements Cloneable{
private String schoolName;
private int stuNums;
private Student stu;
public String getSchoolName() {
return schoolName;
}
public void setSchoolName(String schoolName) {
this.schoolName = schoolName;
}
public int getStuNums() {
return stuNums;
}
public void setStuNums(int stuNums) {
this.stuNums = stuNums;
}
public Student getStu() {
return stu;
}
public void setStu(Student stu) {
this.stu = stu;
}
@Override
protected Object clone() throws CloneNotSupportedException {
School school = (School) super.clone();
school.setSchoolName(new String(getSchoolName()));
school.setStu((Student) stu.clone());
return school;
}
@Override
public String toString() {
return "School{" +
"schoolName='" + schoolName + '\'' +
", stuNums=" + stuNums +
", stu=" + stu +
'}';
}
@Test
public void test1() throws CloneNotSupportedException {
School s1 = new School();
s1.setSchoolName("实验小学");
s1.setStuNums(100);
Student stu1 = new Student();
stu1.setAge(20);
stu1.setName("zhangsan");
stu1.setSex(new StringBuffer("男"));
s1.setStu(stu1);
System.out.println("s1: "+s1);
System.out.println("s1的hashcode:"+s1.hashCode()+" s1中schoolName的hashcode:"+s1.getSchoolName().hashCode()+" s1中stu1的hashcode:"+s1.getStu().hashCode());
School s2 = (School)s1.clone();
System.out.println("s2: "+s2);
System.out.println("s2的hashcode:"+s2.hashCode()+" s2中schoolName的hashcode:"+s2.getSchoolName().hashCode()+" s2中stu1的hashcode:"+s2.getStu().hashCode());
System.out.println("s1.getSchoolName().equals(s2.getSchoolName()):"+s1.getSchoolName().equals(s2.getSchoolName()));
System.out.print("s1.getSchoolName()==s2.getSchoolName()");
System.out.println(s1.getSchoolName()==s2.getSchoolName());
}
}
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| s1: School{schoolName='实验小学', stuNums=100, stu=Student{name='zhangsan', age=20, sex=男}}
s1的hashcode:1535128843 s1中schoolName的hashcode:737493093 s1中stu1的hashcode:1567581361
s2: School{schoolName='实验小学', stuNums=100, stu=Student{name='zhangsan', age=20, sex=男}}
s2的hashcode:849460928 s2中schoolName的hashcode:737493093 s2中stu1的hashcode:580024961
s1.getSchoolName().equals(s2.getSchoolName()):true
s1.getSchoolName()==s2.getSchoolName()false
|
s1的hashcode不等于s2的hashcode
s1中schoolName的hashcode等于s2中schoolName的hashcode
s1中stu1的hashcode不等于s2中stu1的hashcode
s1.getSchoolName().equals(s2.getSchoolName())为true
s1.getSchoolName()==s2.getSchoolName()为false
