标记接口
标记接口(Marker Interface),又称标签接口(Tag Interface)
仅代表一个标记 不包含任何方法
标记接口是用来判断某个类是否具有某种能力
Cloneable标记接口
此类实现了 Cloneable 接口,以指示 Object.clone 方法可以合法地对该类实例进行按字段复制
如果在没有实现 Cloneable 接口的实例上调用 Object 的 clone 方法, 则会导致抛出 CloneNotSupportedException 异常
// Cloneable源码:
public interface Cloneable { }
// 仅代表一个标记
// 克隆的前提条件:
// 被克隆的对象必须实现Cloneable接口
// 必须重写clone方法
基本使用
public class CloneableDemo {
public static void main(String[] args) throws CloneNotSupportedException {
// ArrayList类实现了Cloneable接口
ArrayList<String> list = new ArrayList<String>();
list.add("张三");
list.add("李四");
list.add("王五");
ArrayList<String> listClone = (ArrayList<String>) list.clone();
System.out.println(list == listClone);
System.out.println(listClone);
}
}
Clone案例:将一个学生的数据复制到另一个学生对象中,并且两个对象不受任何的影响.
传统方式:
public class CloneTest {
public static void main(String[] args) {
//传统方式:
Student stu1 = new Student("张三", 12);
//再次创建一个新的学生对象
Student stu2 = new Student();
//把stu1对象name的值取出来赋值给stu2对象的name
stu2.setName(stu1.getName());
//把stu1对象age的值取出来赋值给stu2对象的age
stu2.setAge(stu1.getAge());
System.out.println(stu1 == stu2);
System.out.println(stu1);
System.out.println(stu2);
System.out.println("================");
stu1.setName("李四");
System.out.println(stu1);
System.out.println(stu2);
}
}
class Student {
private String name;
private int age;
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 Student(String name, int age) {
this.name = name;
this.age = age;
}
public Student() {
}
@Override
public String toString() {
return "Student{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}
此时修改对象1的姓名与对象2的姓名无关
克隆方式(浅拷贝):
/*
实现Cloneable接口
重写clone方法 将访问权限改为public 并将返回值类型改为Student
*/
class Student implements Cloneable{
private String name;
private int age;
public Student(String name, int age) {
this.name = name;
this.age = age;
}
@Override
public Student clone() throws CloneNotSupportedException {
return (Student) super.clone();
}
}
class CloneTest01 {
public static void main(String[] args) throws CloneNotSupportedException {
//克隆方式
//创建学生对象
Student stu1 = new Student("张三",12);
//通过克隆获得一个student对象
Student stu2 = stu1.clone();
System.out.println(stu1 == stu2);
System.out.println(stu1);
System.out.println(stu2);
stu1.setName("李四");
System.out.println(stu1);
System.out.println(stu2);
}
}
浅拷贝的局限性:基本数据类型(包括String)可以达到完全复制,引用数据类型则不可以;
class Student implements Cloneable{
private String name;
private int age;
private Car car;
@Override
public Student clone() throws CloneNotSupportedException {
return (Student) super.clone();
}
}
class Car {
private String brand;
public Car() {
}
public Car(String brand) {
this.brand = brand;
}
public String getBrand() {
return brand;
}
public void setBrand(String brand) {
this.brand = brand;
}
@Override
public String toString() {
return "Car{" +
"brand='" + brand + '\'' +
'}';
}
}
class CloneTest02 {
public static void main(String[] args) throws CloneNotSupportedException {
//克隆方式