java设计模式之策略模式(strategy)

一、首先我们要了解到策略模式中它有四种角色：

1、抽象策略，也就是策略接口类或者策略抽象类。

2、具体策略，就是策略实现类。

3、策略执行者。

4、策略使用者。

二、接下来看看下面四个小案例：

1、对一组人的身高进行排序。

抽象策略

package com.liuyc.designpattern.strategy;

public class PersonHeightSortStrategy implements SortStrategy{

    @Override
    public int compareTo(Person t1, Person t2) {
        if(t1.getHeight()>t2.getHeight()){
            return 1;
        }else {
            return 0;
        }
    }
}

具体策略类

package com.liuyc.designpattern.strategy;

public class PersonHeightSortStrategy implements SortStrategy{

    @Override
    public int compareTo(Person t1, Person t2) {
        if(t1.getHeight()>t2.getHeight()){
            return 1;
        }else {
            return 0;
        }
    }
}

策略执行者

package com.liuyc.designpattern.strategy;

public class SortHelper {

    public void sort(T [] t ,SortStrategy sortStrategy){
        //选择排序法
        //第一个循环，控制比较次数
        for (int i = 0 ; i < t.length -1 ; i ++ ){
            //第2个循环，从左往右找出最大的数字
            int tempMaxIndex = i;
            for (int j = i+1 ;j < t.length ; j ++){
                tempMaxIndex = sortStrategy.compareTo(t[j],t[tempMaxIndex]) > 0 ? j:tempMaxIndex;
            }
            //每一次找出最大数字放到已排好序的数字最右边
            T temp = t[i];
            t[i] = t[tempMaxIndex];
            t[tempMaxIndex] = temp;
        }
    }
}

策略使用者

        Person person1 = new Person(100, 500);
        Person person2 = new Person(200, 400);
        Person person3 = new Person(300, 200);
        Person [] peoples = new Person[]{person1,person2,person3};

        SortHelper sortHelper2 = new SortHelper();
        //2、使用按身高排序策略(从高到矮)
        sortHelper2.sort(peoples,new PersonHeightSortStrategy());
        for (int i = 0; i < peoples.length; i++) {
            System.out.println(peoples[i]);
        }

person类

package com.liuyc.designpattern.strategy;

public class Person {
    /**
     * 身高
     */
    private int height;

    /**
     * 体重
     */
    private int weight;

    public Person(int height, int weight) {
        this.height = height;
        this.weight = weight;
    }

    public int getHeight() {
        return height;
    }

    public void setHeight(int height) {
        this.height = height;
    }

    public int getWeight() {
        return weight;
    }

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

    @Override
    public String toString() {
        return "Person{" +
                "height=" + height +
                ", weight=" + weight +
                '}';
    }
}

2、对一组人的体重进行排序，只需要提供具体策略即可。

具体策略类

package com.liuyc.designpattern.strategy;

public class PersonWeightSortStrategy implements SortStrategy{

    @Override
    public int compareTo(Person t1, Person t2) {
        if(t1.getWeight()>t2.getWeight()){
            return 1;
        }else {
            return 0;
        }
    }
}

策略使用者

        Person person1 = new Person(100, 500);
        Person person2 = new Person(200, 400);
        Person person3 = new Person(300, 200);
        Person [] peoples = new Person[]{person1,person2,person3};        
        //3、使用按体重排序策略(重到轻)
        sortHelper2.sort(peoples,new PersonWeightSortStrategy());
        for (int i = 0; i < peoples.length; i++) {
            System.out.println(peoples[i]);
        }

3、对一个double数据进行排序，从大到小，只需要提供具体策略即可。

具体策略类

package com.liuyc.designpattern.strategy;

public class DoubleArraySortStrategy implements SortStrategy{
    @Override
    public int compareTo(Double t1, Double t2) {
        if(t1 > t2){
            return 1;
        }else{
            return -1;
        }
    }
}

策略使用者

        //4、给double数组排序
        Double [] doubles = {31d,11d,25d,91d,43d,10d,5d};

        SortHelper sortHelper3 = new SortHelper();
        sortHelper3.sort(doubles,new DoubleArraySortStrategy());

        for (int i = 0; i < doubles.length; i++) {
            System.out.print(doubles[i] +"  ");
        }

有问题欢迎留言，谢谢！