Java的对象拷贝-Clone

Clone可以拷贝出一个对象的副本，它有分浅拷贝（Shallow copy）和深拷贝（Deep copy),
Clone是如何进行拷贝呢？
1：Object类本身是不实现Cloneable接口的，所以在类为 Object 的对象上调用 clone 方法将会导致在运行时抛出CloneNotSupportedException。
2：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Shallow Clone.对于对象中基本类型的变量，浅拷贝（Shallow copy）是没问题的，但是对于一些reference变量，尽管经过clone之后会产生一个新的reference变量，但它和原始对象中对应的域指向同一个reference对象，它和原始对象中对应的域指向同一个Date对象。
例子：
Grade实体类：

package objectclone;


public class Grade implements Cloneable {
  private String grade;
  private int number;

    public String getGrade() {
        return grade;
    }

    public void setGrade(String name) {
        this.grade = name;
    }

    public int getNumber() {
        return number;
    }

    public void setNumber(int number) {
        this.number = number;
    }
    public Object Clone(){
        try{
            super.clone();
            return super.clone();
        }
        catch(Exception e){
            return null;
        }
    }
}

Person实体类：

package objectclone;

public class Person implements Cloneable{
    private String sex;
    private int age;
    public  Grade c;

    public Person(String sex,int age,Grade c){
        this.sex=sex;
        this.age = age;
        this.c = c;
    }
    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public Grade getC() {
        return c;
    }

    public void setC(Grade c) {
        this.c = c;
    }
    public Object Clone(){
        try{
            super.clone();
            return super.clone();
        }
        catch(Exception e){
            return null;
        }
    }
}

package objectclone;

public class ShallowClone{
    public static void main(String[] args) throws CloneNotSupportedException{
        Grade c = new Grade();
        Person person = new Person("male",25,c);
        Person personcopy = (Person)person.Clone();
        person.c.setGrade("grade1");
        personcopy.c=(Grade)person.c.Clone();//对reference对象进行拷贝
        personcopy.c.setGrade("grade2");
        personcopy.setSex("female");
        personcopy.setAge(24);
        System.out.print("person sex :"+person.getSex());
        System.out.println("   personcopy sex:"+personcopy.getSex());
        System.out.print("person age："+person.getAge());
        System.out.println("   personcopy age："+personcopy.getAge());
        System.out.print("person grade:"+person.c.getGrade());
        System.out.print("    personcopy grade:"+personcopy.c.getGrade());
    }

}

以上执行结果：
person sex :male personcopy sex:female
person age：25 personcopy age：24
person grade:grade1 personcopy grade:grade2
若" //personcopy.c=(Grade)person.c.Clone();",执行结果未：
person sex :male personcopy sex:female
person age：25 personcopy age：24
person grade:grade2 personcopy grade:grade2