Cloneable接口的使用

Cloneable接口声明中没有指定要实现的方法，一个类要实现Cloneable，最好是覆盖Object类的clone()方法。 


1. 如果类没有实现Cloneable接口，调用类对象的clone方法抛出CloneNotSupportedException。 

public class CloneableTest {

    public static void main(String[] args) throws CloneNotSupportedException {
        CloneableTest test = new CloneableTest();
        Object obj = test.clone();
    }
}

结果是抛出CloneNotSupportedException异常 


2. 我们无法定义一个类数组实现了Cloneable, 所以数组默认是实现了Cloneable接口。 

// Invalid definition
public class Person[] implements Cloneable

int[] iMarks = new int[] { 4, 7, 1 , 8 };
int[] copyofiMarks = iMarks.clone();

运行没问题。 


3. Object提供的clone方法是浅度复制 (shallow copy)。 

public class Name {
    private String firstName;
    private String lastName;
    // Omit the getters and setters as well as constructors
}

public class Person implements Cloneable {
    private Name name;
    private int age;
    // Omit the getters and setters as well as constructors

    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

Name name = new Name("John", "Chen");
Person person = new Person(name, 28);
Person copyOfPerson = (Person)person.clone();
name.setFirstName("Johnny");
name.setLastName("Qin");
person.setAge(29);
System.out.println(copyOfPerson.getName().getFirstName() + " " +
        copyOfPerson.getName().getLastName() +
        " " + copyOfPerson.getAge());

结果是：Johnny Qin 28 

对于原型类型（如int），clone是没问题的，被clone的对象改变了不会影响到复制品（age还是28）。 

对于引用类型（如Name），clone方法只是复制了引用（浅度就体现在这），如果改变了引用的值，复制品也会受到影响（Johnny Qin）。 


4. 继承链上的祖先必须要有一个类声明实现Cloneable接口。 

public class Person {
}

public class Male extends Person implements Cloneable {
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

public class ChineseMale extends Male {
}

Person person = new Person();
Male male = new male();
ChineseMale chineseMale = new ChineseMale();
person.clone();
male.clone();
chineseMale.clone();

person.clone()会报错。 


5. Object类本身没有实现Cloneable接口，在一个Object类对象上调用clone方法会报CloneNotSupportedException。