在子类中使用构造函数中的Builder模式

Question

我目前正在使用Builder模式，紧跟在Wikipedia文章 Builder模式
http://en.wikipedia.org/wiki/Builder_pattern中建议的Java实现

这是一个示例代码，说明了我的实现

public class MyPrimitiveObject {
  private String identifier="unknown";
  public static class Builder {
    private final MyPrimitiveObject obj = new MyPrimitiveObject();
    public MyPrimitiveObject build() { return obj; }
    public Builder setidentifier (String val) {
     obj.identifier = val;
     return this;
    }
  }
  public static Builder createBuilder() { return new Builder(); }
  @Override public String toString() { return "ID: "+identifier; }
}

在我的一些使用此类的应用程序中，我碰巧发现了非常相似的建筑代码，因此我想将其子类化MyPrimitiveObject，MySophisticatedObject并将所有重复的代码移入其构造函数中。这就是问题所在。

如何调用超类生成器并将其返回的对象分配为我的实例？

public class MySophisticatedObject extends MyPrimitiveObject {
  private String description;
  public MySophisticatedObject (String someDescription) {
    // this should be the returned object from build() !!
    Builder().setidentifier(generateUUID()).build()
    description = someDescription;
  }     
}

Answer 1

您可能需要考虑使用嵌套的MySophisticatedObject.Builderextends
MyPrimitiveObject.Builder，并覆盖其build()方法。在构建器中具有受保护的构造函数，以 接受 要在其上设置值的实例：

public class MyPrimitiveObject {
  private String identifier="unknown";
  public static class Builder {
    private final MyPrimitiveObject obj;
    public MyPrimitiveObject build() { return obj; }
    public Builder setidentifier (String val) {
     obj.identifier = val;
     return this;
    }

    public Builder() {
        this(new MyPrimitiveObject());
    }

    public Builder(MyPrimitiveObject obj) {
        this.obj = obj;
    }
  }
  ...
}

public class MySophisticatedObject extends MyPrimitiveObject {
  private String description;

  public static class Builder extends MyPrimitiveObject.Builder {
    private final MySophisticatedObject obj;
    public Builder() {
      this(new MySophisticatedObject());
      super.setIdentifier(generateUUID());
    }     
    public Builder(MySophisticatedObject obj) {
      super(obj);
      this.obj = obj;
    }

    public MySophisticatedObject build() {
      return obj;
    }

    // Add code to set the description etc.
  }
}