【设计模式-02】Strategy策略模式及应用场景

一、参考资料

• Java 官方文档

Overview (Java SE 18 & JDK 18)module indexhttps://docs.oracle.com/en/java/javase/18/docs/api/index.html

• Java中使用到的策略模式

Comparator、comparable

Comparator (Java SE 18 & JDK 18)declaration: module: java.base, package: java.util, interface: Comparatorhttps://docs.oracle.com/en/java/javase/18/docs/api/java.base/java/util/Comparator.html

Comparable (Java SE 18 & JDK 18)declaration: module: java.base, package: java.lang, interface: Comparablehttps://docs.oracle.com/en/java/javase/18/docs/api/java.base/java/lang/Comparable.html

二、主要设计思想

对更改关闭，对扩展开放，程序更有弹性，可扩展性强。

Extensibility、Scalability

三、应用场景

对任意数据类型的数组进行排序，如对int、double、float以及对象的排序。

1、Cat.java 对象

/*** @description: 猫对象* @author: flygo* @time: 2022/7/4 11:11*/
public class Cat {private int height, weight;public Cat() {}public Cat(int weight, int height) {this.weight = weight;this.height = height;}public int compareTo(Cat c) {if (this.weight < c.weight) return -1;else if (this.weight > c.weight) return 1;else return 0;}@Overridepublic String toString() {return "Cat{" + "height=" + height + ", weight=" + weight + '}';}
}

2、Sorter.java 排序类

/*** @description: 排序对象* @author: flygo* @time: 2022/7/4 11:16*/
public class Sorter {public void sort(Cat[] arr) {for (int i = 0; i < arr.length - 1; i++) {int minPos = i;for (int j = i + 1; j < arr.length; j++) {minPos = arr[j].compareTo(arr[minPos]) == -1 ? j : minPos;}swap(arr, i, minPos);}}static void swap(Cat[] arr, int i, int j) {Cat temp = arr[i];arr[i] = arr[j];arr[j] = temp;}
}

3、StrategyMain 主类

import java.util.Arrays;/*** @description: 主方法* @author: flygo* @time: 2022/7/4 11:15*/
public class StrategyMain {public static void main(String[] args) {//    int[] arr = {2, 4, 3, 6, 10, 1};Cat[] arr = {new Cat(3, 3), new Cat(5, 5), new Cat(1, 1)};Sorter sorter = new Sorter();sorter.sort(arr);System.out.println(Arrays.toString(arr));}
}

四、使用泛型调整修改

1、定义Comparable接口

注意接口中使用了泛型 <T>，定义了compareTo接口方法。

/*** @description: 比较接口类* @author: flygo* @time: 2022/7/4 15:46*/
public interface Comparable<T> {int compareTo(T o);
}

2、Sorter 排序类

使用Comparable 接口类承接对象数组，只要实现了Comparable接口中compareTo方法，都可以进行排序。

/*** @description: 排序对象* @author: flygo* @time: 2022/7/4 11:16*/
public class Sorter {public void sort(Comparable[] arr) {for (int i = 0; i < arr.length - 1; i++) {int minPos = i;for (int j = i + 1; j < arr.length; j++) {minPos = arr[j].compareTo(arr[minPos]) == -1 ? j : minPos;}swap(arr, i, minPos);}}static void swap(Comparable[] arr, int i, int j) {Comparable temp = arr[i];arr[i] = arr[j];arr[j] = temp;}
}

3、定义一个需要排序的对象，如Dog

Dog对象实现 Comparable 接口类中的 compareTo 方法

/*** @description: 狗* @author: flygo* @time: 2022/7/4 15:48*/
public class Dog implements Comparable<Dog> {int food;public Dog(int food) {this.food = food;}@Overridepublic int compareTo(Dog o) {if (this.food < o.food) return -1;else if (this.food > o.food) return 1;else return 0;}@Overridepublic String toString() {return "Dog{" + "food=" + food + '}';}
}

4、最终效果

最终可以实现对实现Comparable 接口compareTo方法的任意对象进行排序

import java.util.Arrays;/*** @description: 主方法* @author: flygo* @time: 2022/7/4 11:15*/
public class StrategyMain {public static void main(String[] args) {//    int[] arr = {2, 4, 3, 6, 10, 1};//    Cat[] arr = {new Cat(3, 3), new Cat(5, 5), new Cat(1, 1)};Dog[] arr = {new Dog(5), new Dog(1), new Dog(3)};Sorter sorter = new Sorter();sorter.sort(arr);System.out.println(Arrays.toString(arr));}
}

五、源码地址

GitHub - jxaufang168/Design-Patterns: 设计模式学习设计模式学习. Contribute to jxaufang168/Design-Patterns development by creating an account on GitHub.https://github.com/jxaufang168/Design-Patterns