Java clone()

Object 中有一个projected clone() 方法，所以很多类都支持这个“自我克隆”的方法。自定义类想实现clone() 方法只需要实现Cloneable接口即可。它跟Serializable一样，里面没有任何方法，只是一个标志性的接口。一般来讲，利用clone() 可以复制出一个一模一样的实例，而且两者完全隔离。因为它是直接在内存中，将所有数据拷贝一份到另外的区域，效率很高。根据这个原理，我们可以想到这样的问题：如果这个实例包含引用型变量呢？聪明的你应该已经猜到答案了，我们来验证一下。

package testClone;

public class Person {
    public String name;

    public Person(String n) {
        name = n;
    }

}

package testClone;

public class Family implements Cloneable {
    public Person father;
    public Person mother;
    public Person son;
    public int familyNum;

    public Family(Person f, Person m, Person s) {
        father = f;
        mother = m;
        son = s;
        familyNum = 3;
    }

    @Override
    protected Family clone() throws CloneNotSupportedException {
        // TODO Auto-generated method stub
        return (Family) super.clone();
    }

    @Override
    public String toString() {
        // TODO Auto-generated method stub
        return "Father: " + father.name + "; Mother: " + mother.name + " Son: " + son.name + "; " + "Family Number: "
                + familyNum;
    }

}

package testClone;

public class TestClone {

    public static void main(String[] args) {
        Person father = new Person("Dave1");
        Person mother = new Person("Nancy");
        Person son = new Person("Jhon");
        Family f1 = new Family(father, mother, son);
        System.out.println("一开始f1的数据情况是：");
        System.out.println(f1.toString() + "\n");

        father.name = "Dave2";
        System.out.println("通过Person实例，修改father的name:");
        System.out.println(f1.toString() + "\n");

        f1.father.name = "Dave3";
        System.out.println("通过Family实例，修改father的name：");
        System.out.println(f1.toString() + "\n");

        try {
            Family f2 = f1.clone();
            f2.father.name = "Dave4";
            System.out.println("通过f2实例，修改father的name，看一看对f1有影响吗？");
            System.out.println(f1.toString() + "\n");

            f2.familyNum = 6;
            System.out.println("通过f2实例，修改familyNum，看一看对f1有影响吗？");
            System.out.println(f1.toString() + "\n");

        } catch (CloneNotSupportedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

运行结果

所以，对于clone() 要小心成员变量是引用型变量的情况。