Java设计模式---Strategy策略模式

来源：cnblogs　　作者：DingYu　　时间：2018/12/3 10:09:08　　对本文有异议

参考于 :

　　大话设计模式

　　马士兵设计模式视频

1.场景介绍

　　购物网站上有一个产品，有三个字段，档次，价格，重量。

　　有些同学喜欢轻的，有些手头紧，想要便宜的，有些喜欢档次高的。

　　那么我们为了提高网站用户体验，必须给六个按钮，按照价格升序降序，按照档次升序降序，按照重量升序降序。

　（这里只是打个比方，好像一般遇到这种情况是用Lucenc）

2.不用策略模式

package com.dingyu;
import java.util.Arrays;
/**
 * 产品类，这里为了代码代码尽可能的少，set get方法没加
 * Comparable接口中有一个compareTo方法,这个方法进行两个对象比较
 * Arrays.sort内部方法用到了这个compareTo方法
 * 这样以后只要我的类实现了Comparable接口，排序的代码可以通用（Arrays.sort()）去排序，可以自定义比较规则，
 * 
 * @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 "价格 " + price + " 重量：" + weight + " 档次：" + 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 源码:

　　缺点：把compareTo逻辑写死了，如果要改，需要修改compareTo里的逻辑。违反开闭原则。

3.使用策略模式

　　使用一个接口，每个策略都实现这个接口

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;
/**
 * 产品类，这里为了代码代码尽可能的少，set get方法没加 Comparable接口中有一个compareTo方法,这个方法进行两个对象比较
 * Arrays.sort内部方法用到了这个compareTo方法
 * 这样以后只要我的类实现了Comparable接口，排序的代码可以通用（Arrays.sort()）去排序，可以自定义比较规则，
 * 
 * @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 "价格 " + price + " 重量：" + weight + " 档次：" + 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]);
        }
    }
}