我是否正确实现了基于泛型的Java工厂？

Question

我不相信我正在实现工厂模式,因为Application类' createDocument方法接受任何类类型,而不仅仅是子类Document.

换句话说,有没有办法可以限制createDocument方法只接受子类Document？

• Document.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());
      }
  }
  

• Application.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);
          }
      };
  }
  

• Main.java

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

Answer 1

您应该绑定您的泛型,以便它只使用继承Document的T.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();
    };
}

Answer 2

代码看起来不错.在实际实现中,不应声明工厂方法抛出任何与反射相关的异常.无论如何,您可能会有一些不同的代码来创建文档.

例如,faxtory方法应该将a Class<? extends Document>作为其参数,以便人们不能要求它创建一个String.

[更新:]代码示例:

public Document createDocument(Class<? extends Document> clazz) {
  try {
    return clazz.newInstance();
  } catch (InstantiationException e) {
    throw new IllegalArgumentException(e);
  }
}