使用 Java 8 功能介面實現策略模式
此示例的目的是展示如何使用 Java 8 功能介面實現策略模式。我們將從經典 Java 中的簡單用例程式碼開始,然後以 Java 8 方式重新編碼。
我們使用的示例問題是一系列演算法(策略),描述了遠距離通訊的不同方式。
經典 Java 版本
我們的演算法族合同由以下介面定義:
public interface CommunicateInterface {
public String communicate(String destination);
}
然後我們可以實現一些演算法,如下:
public class CommunicateViaPhone implements CommunicateInterface {
@Override
public String communicate(String destination) {
return "communicating " + destination +" via Phone..";
}
}
public class CommunicateViaEmail implements CommunicateInterface {
@Override
public String communicate(String destination) {
return "communicating " + destination + " via Email..";
}
}
public class CommunicateViaVideo implements CommunicateInterface {
@Override
public String communicate(String destination) {
return "communicating " + destination + " via Video..";
}
}
這些可以例項化如下:
CommunicateViaPhone communicateViaPhone = new CommunicateViaPhone();
CommunicateViaEmail communicateViaEmail = new CommunicateViaEmail();
CommunicateViaVideo communicateViaVideo = new CommunicateViaVideo();
接下來,我們實現一個使用該策略的服務:
public class CommunicationService {
private CommunicateInterface communcationMeans;
public void setCommuncationMeans(CommunicateInterface communcationMeans) {
this.communcationMeans = communcationMeans;
}
public void communicate(String destination) {
this.communcationMeans.communicate(destination);
}
}
最後,我們可以使用不同的策略如下:
CommunicationService communicationService = new CommunicationService();
// via phone
communicationService.setCommuncationMeans(communicateViaPhone);
communicationService.communicate("1234567");
// via email
communicationService.setCommuncationMeans(communicateViaEmail);
communicationService.communicate("hi@me.com");
使用 Java 8 功能介面
不同演算法實現的契約不需要專用介面。相反,我們可以使用現有的 java.util.function.Function<T, R>
介面來描述它。
組成 the family of algorithms
的不同演算法可以表示為 lambda 表示式。這取代了策略類和它們的例項。
Function<String, String> communicateViaEmail =
destination -> "communicating " + destination + " via Email..";
Function<String, String> communicateViaPhone =
destination -> "communicating " + destination + " via Phone..";
Function<String, String> communicateViaVideo =
destination -> "communicating " + destination + " via Video..";
接下來,我們可以將服務編碼如下:
public class CommunicationService {
private Function<String, String> communcationMeans;
public void setCommuncationMeans(Function<String, String> communcationMeans) {
this.communcationMeans = communcationMeans;
}
public void communicate(String destination) {
this.communcationMeans.communicate(destination);
}
}
最後,我們使用如下策略
CommunicationService communicationService = new CommunicationService();
// via phone
communicationService.setCommuncationMeans(communicateViaPhone);
communicationService.communicate("1234567");
// via email
communicationService.setCommuncationMeans(communicateViaEmail);
communicationService.communicate("hi@me.com");
甚至:
communicationService.setCommuncationMeans(
destination -> "communicating " + destination + " via Smoke signals.." );
CommunicationService.communicate("anyone");