我是否正确实施了一个基于泛型的Java工厂？ [英] Am I implementing a generics-based Java factory correctly?

问题描述

我不相信我正在实现工厂模式，因为 Application class' createDocument 方法接受任何类型，不只是 Document的子类。

I don't believe I am implementing the factory pattern correctly because the Application class' createDocument method accepts any class type, not just subclasses of Document.

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

In other words, is there a way I can restrict the createDocument method to only accept subclasses of Document?

• Document.java
  
  

• Document.java

package com.example.factory;

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

DrawingDocument.java

DrawingDocument.java

package com.example.factory

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

Application.java

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

Main.java

package com.example.factory;

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

推荐答案

您应该绑定您的通用名称，以便它只使用T继承Document。
例子：

You should bound your generic so that it is only using T's that inherit Document. example:

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

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