1️⃣概念
定义:指原型实例指定创建对象的种类,并且通过拷贝这些原型创建新的对象;
特点:不需要知道任何的创建细节,并且不调用构造函数;
类型:创建型;
2️⃣适用场景
类初始化消耗太多资源;
new产生的一个对象需要非常繁琐的过程(数据准备 访问权限等);
构造函数比较复杂;
循环体中生产大量的对象时;
3️⃣优点
原型模式性能比直接new一个对象性能高;
简化创建过程
4️⃣缺点
必须配备克隆方法;
对克隆复杂对象或者对克隆出的对象进行复杂改造时,容易引入风险;
深拷贝和浅拷贝要运用得当;
5️⃣原型模式Coding
①创建一个发邮件的场景
public class Mail implements Cloneable{
private String name;
private String emailAddress;
private String content;
public Mail(){
System.out.println("Mail Class Constructor");
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getEmailAddress() {
return emailAddress;
}
public void setEmailAddress(String emailAddress) {
this.emailAddress = emailAddress;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
@Override
public String toString() {
return "Mail{" +
"name='" + name + '\'' +
", emailAddress='" + emailAddress + '\'' +
", content='" + content + '\'' +
'}'+super.toString();
}
@Override
protected Object clone() throws CloneNotSupportedException {
System.out.println("clone mail object");
return super.clone();
}
}
②创建MailUtil工具类
public class MailUtil {
public static void sendMail(Mail mail){
String outputContent = "向{0}同学,邮件地址:{1},邮件内容:{2}发送邮件成功";
System.out.println(MessageFormat.format(outputContent,mail.getName(),mail.getEmailAddress(),mail.getContent()));
}
public static void saveOriginMailRecord(Mail mail){
System.out.println("存储originMail记录,originMail:"+mail.getContent());
}
}
③编写测试类
public class Test {
public static void main(String[] args) throws CloneNotSupportedException {
Mail mail = new Mail();
mail.setContent("初始化模板");
System.out.println("初始化mail:"+mail);
for(int i = 0;i < 10;i++){
Mail mailTemp = (Mail) mail.clone();
mailTemp.setName("姓名"+i);
mailTemp.setEmailAddress("姓名"+i+"@test.com");
mailTemp.setContent("恭喜您，此次活动中奖了");
MailUtil.sendMail(mailTemp);
System.out.println("克隆的mailTemp:"+mailTemp);
}
MailUtil.saveOriginMailRecord(mail);
}
}
6️⃣UML类图
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7️⃣深克隆与浅克隆
(1)浅克隆
①创建pig类
public class Pig implements Cloneable{
private String name;
private Date birthday;
public Pig(String name, Date birthday) {
this.name = name;
this.birthday = birthday;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
@Override
protected Object clone() throws CloneNotSupportedException {
Pig pig = (Pig)super.clone();
}
@Override
public String toString() {
return "Pig{" +
"name='" + name + '\'' +
", birthday=" + birthday +
'}'+super.toString();
}
}
②编写测试类
public class Test {
public static void main(String[] args) throws CloneNotSupportedException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
Date birthday = new Date(0L);
Pig pig1 = new Pig("佩奇",birthday);
Pig pig2 = (Pig) pig1.clone();
System.out.println(pig1);
System.out.println(pig2);
pig1.getBirthday().setTime(666666666666L);
System.out.println(pig1);
System.out.println(pig2);
}
}
从结果中可以看出,先打印的pig1与pig2的内容是一致的,在设置完生日以后打印的一组结果内容也是一致的,但是我们发现在我们设置完pig1的生日以后,后打印的一组内容的生日都发生了变化,这又是为什么呢?我们通过debug找到了答案;
通过分析我们找到了原因,pig1与pig2对象所使用的生日属性都是一个对象的,所以我们在修改完生日以后两个对象的内容都发生了变化(也就是说我们引用的克隆对象都是同一个对象,当我们修改被克隆对象的属性的时候,克隆出来的对象属性也会跟着发生变化);这就是浅克隆,同时默认的也是浅克隆;
(2)深克隆
从上边的结论中我们可以得出,默认的克隆方式是浅克隆,那么怎么实现深克隆呢?其实也简单,只要我们对对象的引用类型也添加克隆实现就可以解决了;
@Override
protected Object clone() throws CloneNotSupportedException {
Pig pig = (Pig)super.clone();
//深克隆
pig.birthday = (Date) pig.birthday.clone();
return pig;
}
通过上图我们可以看出在我们进行了引用属性的深克隆以后,最后一组对象的内容已经发生了变化,同时debug的时候内存中引用的对象也发生了变化,效果已经达到了我们的预期;
注意:在使用原型模式的时候一定要进行深克隆,否则可能会出现Bug
8️⃣原型模式破坏单例
①使用HungrySingleton
public class HungrySingleton implements Serializable,Cloneable{
private final static HungrySingleton hungrySingleton;
static{
hungrySingleton = new HungrySingleton();
}
private HungrySingleton(){
if(hungrySingleton != null){
throw new RuntimeException("单例构造器禁止反射调用");
}
}
public static HungrySingleton getInstance(){
return hungrySingleton;
}
private Object readResolve(){
return hungrySingleton;
}
@Override
protected Object clone() throws CloneNotSupportedException {
return super.clone();
}
}
②编写测试类
public class Test {
public static void main(String[] args) throws CloneNotSupportedException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
HungrySingleton hungrySingleton = HungrySingleton.getInstance();
Method method = hungrySingleton.getClass().getDeclaredMethod("clone");
method.setAccessible(true);
HungrySingleton cloneHungrySingleton = (HungrySingleton) method.invoke(hungrySingleton);
System.out.println(hungrySingleton);
System.out.println(cloneHungrySingleton);
}
}
可以看到通过使用clone我们依旧破坏了单例,那要如何才能解决这个问题呢?
①单例类不实现Cloneable接口;
②单例类在重写clone方法时不使用默认的实现,将其修改为
@Override
protected Object clone() throws CloneNotSupportedException {
return getInstance();
}
可以看到通过以上的修改,再次运行测试类的时候两个对象就完全是一致的了;
9️⃣原型模式的实际应用
①JDK中原型模式的使用
public class ArrayList<E> extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
/**
* Returns a shallow copy of this <tt>ArrayList</tt> instance. (The
* elements themselves are not copied.)
*
* @return a clone of this <tt>ArrayList</tt> instance
*/
public Object clone() {
try {
ArrayList<?> v = (ArrayList<?>) super.clone();
v.elementData = Arrays.copyOf(elementData, size);
v.modCount = 0;
return v;
} catch (CloneNotSupportedException e) {
// this shouldn't happen, since we are Cloneable
throw new InternalError(e);
}
}
