策略模式允許在允許中替換算法。要實現該解決方案,需要將每個算法表示爲Strategy(策略)類。然後應用程序委託當前的Strategy類來執行特定於策略的算法。
1、Strategy
下面示例使用Role(充當Strategy)接口來聲明策略行爲和倆個具體來——Buyer和Seller來實現不同的行爲:
Role接口:
package strategy;
public interface Role {
public boolean siSatisfied(Product product, double price);
}
Seller類:希望銷售的產品都設置了20%的利潤率
package strategy;
public class Seller implements Role{
public boolean siSatisfied(Product product, double price) {
//具有20%的利潤
if(price - product.getCost() > product.getCost() * .2){
return true;
}else{
return false;
}
}
}
對於Buyer來說,他要買下此種商品,必須有一個限制額。
package strategy;
public class Buyer implements Role{
private double limit;
public Buyer(double limit){
this.limit = limit;
}
public boolean siSatisfied(Product product, double price) {
if(price < limit && price < product.getCost() * 2){
return true;
}
return false;
}
}
2、context
Context這裏是指:管理Role的Person類。Person類與Role接口又一個關聯,另外值得注意的是,Role又一個setter和getter方法,它允許一個人的角色在程序執行時發生變化。以後,其它的Role實現對象(如broker(中間)等)都可以被添加。因爲它們對特定的子類沒有依賴。下面時Person類:
package strategy;
public class Person {
private String name;
private Role role;
public Person(String name){
this.name = name;
}
public Role getRole(){
return role;
}
public void setRole(Role role){
this.role = role;
}
public boolean statisfied(Product product, double price){
//statisfied方法將特定於角色的行爲委託給其Role接口。這裏多態會選擇正確的底層對象。
return role.isSatisfied(product, price);
}
}
其它類:本示例的Product類及執行的Main類:
1、Product
package strategy;
public class Product {
private String name;
private String description;
private double cost;
public Product(String name, String description, double cost){
this.name = name;
this.description = description;
this.cost = cost;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
public double getCost() {
return cost;
}
public void setCost(double cost) {
this.cost = cost;
}
}
2、Main類
package strategy;
public class Main {
public static void main(String[] args){
Product house = new Product("house", "Three room and a parlor", 200000);
Product laptop = new Product("laptop", "The latest style of lenovo laptop computer", 10000);
Person liLei = new Person("李雷");
Person hanMeimei = new Person("韓梅梅");
liLei.setRole(new Buyer(500000));
hanMeimei.setRole(new Seller());
if(!hanMeimei.statisfied(house, 200000)){
System.out.println("韓梅梅房子不會賣200000。");
}
if(!liLei.statisfied(house, 6000000)){
System.out.println("李雷,覺得如果要花6000000買下那房子,太貴了!");
}
if(liLei.statisfied(house, 390000) && hanMeimei.statisfied(house, 390000)){
System.out.println("他們最終已390000的價格成交了!");
//允許時修改一個對象的行爲而不影響它的實現
hanMeimei.setRole(new Buyer(390000));
if(hanMeimei.statisfied(laptop, 11000)){
System.out.println("得到390000,韓梅梅現在花了11000去買進了一臺最新款的聯繫筆記本!");
}
}
}
}
通過實現策略模式,可以在運行時修改一個對象的行爲而不影響它的實現。這是軟件設計中非常強大的工具。