java - 在子类的构造函数中使用构建器模式

Question

我目前正在使用构建器模式，密切关注维基百科文章构建器模式中建议的 Java 实现 http://en.wikipedia.org/wiki/Builder_pattern

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; }
}

在我的一些使用这个类的应用程序中，我碰巧发现非常相似的构建代码，所以我想在 MySophisticatedObject 中继承 MyPrimitiveObject 并移动我所有重复的代码进入它的构造函数..这就是问题所在。

我如何调用父类(super class) Builder 并将其返回的对象指定为我的实例？

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

您可能需要考虑拥有一个嵌套的 MySophisticatedObject.Builder，它扩展了 MyPrimitiveObject.Builder，并覆盖了它的 build() 方法。在构建器中有一个 protected 构造函数来接受要设置值的实例:

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.
  }
}