建立型模式之原型模式(2.3)

noneplus發表於2019-08-12

什麼是原型模式?

簡單來說,通過複製的方式建立物件。(被複制的物件可以理解為模板)


原型模式的應用場景

複雜結構物件的建立。

複雜結構物件:可以理解為物件裡面還有物件。


【舉個栗子】:點外賣的收貨地址


收貨地址包括姓名,電話和住址。第一次點外賣的時候需要完整的填寫這些資訊,但是之後點的過程基本上是不用再重新填寫這些資訊的。試想一下,每次下單之前都要填一遍姓名,電話,詳細地址(假設省市已經定位好了)。頭大.....而這個場景,正是原型模式的用武之地。

點外賣之前複製上一次填寫的地址,直接下單;或者手機號出現變更,修改一下直接更新到模板即可。

原型模式的本質是建立一個物件模板,然後通過複製的方式實現複用。


深拷貝(複雜物件一波帶走)

在深拷貝之前,簡單聊一下淺拷貝。

以上述收貨地址為例,如果只涉及到姓名,電話這些基本資料型別(淺拷貝與深拷貝是基本沒有區別的),但是如果涉及到地址這樣的引用型別。淺拷貝就會出現問題。淺拷貝對於引用物件,只複製其引用地址。所以複製出來的物件和被複制的物件會指向同一個值。假設你想建立兩個收貨模板,地址是不同的,那麼就只能使用深拷貝了。


擼段程式碼試試看:

思路:

1.建立Info類和Address類繼承Serializable介面,為了後面實現序列化寫入記憶體。(實現平臺無關性)

2.Info類還需要繼承Cloneable介面,並重寫clone()方法,注:protected改為public

3.在clone()方法中新增寫入記憶體和讀取的邏輯

4.Info info1 = (Info) info.clone();建立物件,並可做靈活修改。

import java.io.*;

class Address implements  Serializable
{
    private String province;
    private String city;
    private String Street;
    private String door_number;

    public Address(String province, String city, String street, String door_number) {
        this.province = province;
        this.city = city;
        Street = street;
        this.door_number = door_number;
    }

    public String getProvince() {
        return province;
    }

    public void setProvince(String province) {
        this.province = province;
    }

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public String getStreet() {
        return Street;
    }

    public void setStreet(String street) {
        Street = street;
    }

    public String getDoor_number() {
        return door_number;
    }

    public void setDoor_number(String door_number) {
        this.door_number = door_number;
    }

    @Override
    public String toString() {
        return "Address{" +
                "province='" + province + '\'' +
                ", city='" + city + '\'' +
                ", Street='" + Street + '\'' +
                ", door_number='" + door_number + '\'' +
                '}';
    }
}

class Info implements Cloneable, Serializable   //1.建立一個外賣資訊類,繼承Cloneable(可複製),Serializable(可序列化)
{
    private String name;
    private String number;

    Address address;

    public String getName() {
        return name;
    }

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

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    public Address getAddress() {
        return address;
    }

    public void setAddress(Address address) {
        this.address = address;
    }

    public Info(String name, String number, Address address) {
        this.name = name;
        this.number = number;
        this.address = address;
    }

    @Override
    public String toString() {
        return "Info{" +
                "name='" + name + '\'' +
                ", number='" + number + '\'' +
                ", address=" + address +
                '}';
    }

    @Override
    public Object clone() throws CloneNotSupportedException {    //2.重寫clone方法,並把protected換成public
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        try {
                ObjectOutputStream oos = new ObjectOutputStream(out);
                oos.writeObject(this);   //寫入記憶體
                oos.close();

            byte[] bytes = out.toByteArray();
            InputStream in = new ByteArrayInputStream(bytes);
            ObjectInputStream ois = new ObjectInputStream(in);
            Object clone = ois.readObject();  //讀取記憶體
            ois.close();

            return clone;

        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

}

/*
clone()方法直接複製在記憶體中已經建立物件的二進位制,效率極高!(不需要呼叫構造器)

protected native Object clone() throws CloneNotSupportedException;
native修飾的方法直接呼叫底層的C語言

 */
public class MyInfo
{
    public static void main(String[] args) throws CloneNotSupportedException {
        Info info = new Info("shadow","18116207310",new Address("上海","浦東新區","振南路","355"));
        System.out.println(info);
        Info info1 = (Info) info.clone();  //3.複製加強轉
        System.out.println(info1);

        System.out.println("//修改電話:");
        Info info2 = (Info) info.clone();
        info2.setNumber("123456789");
        System.out.println(info2);

        System.out.println("//修改地址:");
        Info info3 = (Info) info.clone();
        info3.getAddress().setStreet("西語街");
        info3.getAddress().setDoor_number("666");

        System.out.println(info3);
    }
}

輸出結果:

1565608154656

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