cURL没有获取URL的HTML源代码(cURL not getting HTML source of URL)

 你可以使用组合而不是继承。 
 
 想法1 
 
 PathData类可能包含对Path和ExtendedPathData的引用： 
 
// encapsulate properly in your code, this is
// just a short sample
class PathData {
  public Path path;
  public ExtendedPathData data;
}
 
 这使您可以将data成员设置为null 。 每个PathData实例的大小始终为两个引用。 当ExtendedPathData的成员数量增加时，实际的内存消耗只会增长为具有非空data PathData实例。 
 
 想法2 
 
 你可以通过使用两个实现的接口来删除更多的参考： 
 
interface PathData {
  Path path();
  ExtendedPathData data();
}

final class NullPathData implements PathData {
  Path path;
  public Path path() { return path; }
  public ExtendedPathData data() { return null; }
}

final class ExtendedPathData implements PathData {
  Path path;
  ExtendedPathData data;
  public Path path() { return path; }
  public ExtendedPathData data() { return data; }
}
 
 由您决定是否有两个实现真的值得代码，因为您需要一个工厂方法来决定使用哪个实现。 它是每个实例的一个 4字节参考... 
 
 更多的东西 
 
 如果ExtendedPathData是不可变的，并且可能存在许多相同的实例 ，则还可以通过公开使用实例池而不是公共构造函数的静态工厂方法来将它们池化 。 
 
 如果你有Joshua Bloch的Effective Java ，下面是更详细的解释提示的更多参考资料（在更一般的上下文中）： 
 
 
 
 项目1考虑静态工厂方法而不是构造函数 
 
 
 项目16赞成继承 
 

You could use composition instead of inheritance.
 
Idea 1
 
A PathData class might contain a reference to a Path and a ExtendedPathData:
 
// encapsulate properly in your code, this is
// just a short sample
class PathData {
  public Path path;
  public ExtendedPathData data;
}
 
This enables you to set the data member to null. Each PathData instance has a size of constantly two references. When the number of members in ExtendedPathData grows, the actual memory consumption grows only for PathData instances that have a non-null data.
 
Idea 2
 
You could shave off one more reference by using an interface with two implementations:
 
interface PathData {
  Path path();
  ExtendedPathData data();
}

final class NullPathData implements PathData {
  Path path;
  public Path path() { return path; }
  public ExtendedPathData data() { return null; }
}

final class ExtendedPathData implements PathData {
  Path path;
  ExtendedPathData data;
  public Path path() { return path; }
  public ExtendedPathData data() { return data; }
}
 
It's up to you to decide whether having two implementations is really worth the code, as you need a factory method here to decide what implementation to use. It's one 4-byte-reference per instance...
 
Further stuff
 
If ExtendedPathData is immutable and many equal instances may exist, you could also pool them by exposing a static factory method that uses an instance pool instead of a public constructor.
 
In case you've got Effective Java by Joshua Bloch, here are further references explaining the tips in detail (in a more general context):
 
 
 
Item 1 Consider static factory methods instead of constructors
 
 
Item 16 Favor composition over inheritance