java - 我是否正确地实现了基于泛型的 Java 工厂？

Question

我认为我没有正确实现工厂模式，因为 Application 类的 createDocument 方法接受任何类类型，而不仅仅是 Document< 的子类.

换句话说，有没有办法限制 createDocument 方法只接受 Document 的子类？

• 文档.java

  package com.example.factory;
  
  public abstract class Document {
      public Document() {
          System.out.println("New Document instance created: " + this.toString());
      }
  }
  

• DrawingDocument.java

  package com.example.factory
  
  public class DrawingDocument extends Document {
      public DrawingDocument() {
          System.out.println("New DrawingDocument instance created: " this.toString());
      }
  }
  

• 应用程序.java

  package com.example.factory;
  
  public class Application {
      public <T> T createDocument(Class<T> documentClass) {
          try {
              return documentClass.newInstance();
          } catch (InstantiationException e) {
              throw new IllegalArgumentException(e);
          } catch (IllegalAccessException e) {
              throw new IllegalArgumentException(e);
          }
      };
  }
  

• 主.java

  package com.example.factory;
  
  public static void main(String[] args) {
      Application application = new Application();
      application.createDocument(DrawingDocument.class);
  }
  

Answer 1

你应该 bound您的泛型，以便它仅使用继承 Document 的 T。示例:

public class Application {
    //Add extends Document after T
    public static <T extends Document> T createDocument(Class<T> documentClass) throws InstantiationException, IllegalAccessException {
        return documentClass.newInstance();
    };
}