Java設計模式---Strategy策略模式

參考於 :

　　大話設計模式

　　馬士兵設計模式視頻

1.場景介紹

　　購物網站上有一個產品，有三個欄位，檔次，價格，重量。

　　有些同學喜歡輕的，有些手頭緊，想要便宜的，有些喜歡檔次高的。

　　那麼我們為了提高網站用戶體驗，必須給六個按鈕，按照價格升序降序，按照檔次升序降序，按照重量升序降序。

　（這裡只是打個比方，好像一般遇到這種情況是用Lucenc）

2.不用策略模式

package com.dingyu;

import java.util.Arrays;

/**
 * 產品類，這裡為了代碼代碼儘可能的少，set get方法沒加
 * Comparable介面中有一個compareTo方法,這個方法進行兩個對象比較
 * Arrays.sort內部方法用到了這個compareTo方法
 * 這樣以後只要我的類實現了Comparable介面，排序的代碼可以通用（Arrays.sort()）去排序，可以自定義比較規則，
 * 
 * @author dingyu
 *
 */
public class Product implements Comparable<Product> {
    private double quality;
    private double price;
    private int weight;

    public Product(double quality, double price, int weight) {
        this.quality = quality;
        this.price = price;
        this.weight = weight;
    }
    
    @Override
    public int compareTo(Product product) {
        if (this.price > product.price)
            return 1;
        else if (this.price == product.price)
            return 0;
        else
            return -1;             
    }

    @Override
    public String toString() {
        return "價格 " + price + " 重量：" + weight + " 檔次：" + quality;
    }

    public static void main(String[] args) {
        Product[] people = { new Product(2, 500, 50), new Product(3, 1000, 60), new Product(1, 200, 70) };
        Arrays.sort(people);
        for (int i = 0; i < people.length; i++) {
            System.out.println(people[i]);
        }
    }
}

　　JDK 源碼:

 　　缺點：把compareTo邏輯寫死了，如果要改，需要修改compareTo里的邏輯。違反開閉原則。

3.使用策略模式

　　使用一個介面，每個策略都實現這個介面

package com.dingyu;

public interface Comparator<T> {
    public int compare(T t1,T t2);
}

package com.dingyu;

public class CompareHeight implements Comparator<Product> {

    @Override
    public int compare(Product t1, Product t2) {

        if (t1.getPrice() > t2.getPrice())
            return 1;
        else if (t1.getPrice() == t2.getPrice())
            return 0;
        else
            return -1;
    }

}

package com.dingyu;

public class CompareQunatity implements Comparator<Product>{

    @Override
    public int compare(Product t1, Product t2) {
        if (t1.getQuality() > t2.getQuality())
            return 1;
        else if (t1.getQuality() == t2.getQuality())
            return 0;
        else
            return -1;
    }

}

package com.dingyu;

public class CompareWeight implements Comparator<Product> {

    @Override
    public int compare(Product t1, Product t2) {
        if (t1.getWeight() > t2.getWeight())
            return 1;
        else if (t1.getWeight() == t2.getWeight())
            return 0;
        else
            return -1;
    }

}

package com.dingyu;

import java.util.Arrays;

/**
 * 產品類，這裡為了代碼代碼儘可能的少，set get方法沒加 Comparable介面中有一個compareTo方法,這個方法進行兩個對象比較
 * Arrays.sort內部方法用到了這個compareTo方法
 * 這樣以後只要我的類實現了Comparable介面，排序的代碼可以通用（Arrays.sort()）去排序，可以自定義比較規則，
 * 
 * @author dingyu
 *
 */
public class Product implements Comparable<Product> {
    private double quality;
    private double price;
    private int weight;
    private static Comparator<Product> comparator;

    public Product(double quality, double price, int weight) {
        this.quality = quality;
        this.price = price;
        this.weight = weight;
    }

    public double getQuality() {
        return quality;
    }

    public void setQuality(double quality) {
        this.quality = quality;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public int getWeight() {
        return weight;
    }

    public void setWeight(int weight) {
        this.weight = weight;
    }

    public static Comparator<Product> getComparator() {
        return comparator;
    }

    public static void setComparator(Comparator<Product> comparator) {
        Product.comparator = comparator;
    }

    @Override
    public int compareTo(Product product) {
        return comparator.compare(this, product);
    }

    @Override
    public String toString() {
        return "價格 " + price + " 重量：" + weight + " 檔次：" + quality;
    }

    public static void main(String[] args) {
        Product[] products = { new Product(2, 500, 50), new Product(3, 1000, 60), new Product(1, 200, 70) };
        Product.setComparator(new CompareHeight());
        Arrays.sort(products);
        for (int i = 0; i < people.length; i++) {
            System.out.println(people[i]);
        }
    }
}