在 Java 中扩展现有对象以实现 Comparable

发布于 2025-01-02 16:36:51 字数 496 浏览 1 评论 0原文

目前我的问题是我需要使用一个不允许更改的现有框架，解决我的问题最方便的方法是使用 Comparable 对象。假设我有一个对象 Foo，它没有实现 Comparable，并且不允许我进去更改它以使其成为 Comparable。我的想法是只使用 Bar，它扩展了 Foo 并实现了 Comparable。

public class Bar extends Foo implements Comparable
{
   public int compareTo( Object o)
   {
      Foo f = (Foo) o;
      if( this.getID() < f.getID() ) return -1;
      else if ( this.getID() == f.getID() ) return 0;
      else return -1;
   }
}

但假设我在某处得到了 Foo 的实例。如何将其变成 Bar 的实例？针对这种情况是否有推荐的替代解决方案？

原文

Currently my issue is that I need to use an existing framework which I am not allowed to change, and the most convenient way to solve my problem is to use Comparable objects. Suppose I have an object Foo, which does not implement Comparable, and I'm not allowed to go in and change it to make it Comparable. My idea was to just use Bar, which extends Foo and implements Comparable.

public class Bar extends Foo implements Comparable
{
   public int compareTo( Object o)
   {
      Foo f = (Foo) o;
      if( this.getID() < f.getID() ) return -1;
      else if ( this.getID() == f.getID() ) return 0;
      else return -1;
   }
}

But then suppose I get an instance of Foo somewhere. How do I turn it into an instance of Bar? Is there an a recommended alternative solution to this situation?

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绮烟 2025-01-09 16:36:51

如果您绝对需要 Comparable，而不是 Comparator，请使用装饰器（如其他人提到的）

public class ComparableFoo implements Comparable<ComparableFoo> {

   final Foo foo;

   public ComparableFoo(Foo foo) {
      this.foo = foo;
   }

   @Override
   public int compareTo(ComparableFoo o) {
      Foo other = o.foo;
      // do comparison here, e.g.
      return foo.getDate().compareTo(other.getDate());
   }

}

请注意，ComparableFoo 不需要扩展 Foo。在某些情况下，这可能很好，但不是必需的。如果您确实想获取底层 Foo，则可以将其放在一个字段中，并且您可以访问该字段，或者提供一个正式的访问器。

If you absolutely need a Comparable, not a Comparator, use a Decorator (as mentioned by others)

public class ComparableFoo implements Comparable<ComparableFoo> {

   final Foo foo;

   public ComparableFoo(Foo foo) {
      this.foo = foo;
   }

   @Override
   public int compareTo(ComparableFoo o) {
      Foo other = o.foo;
      // do comparison here, e.g.
      return foo.getDate().compareTo(other.getDate());
   }

}

Note that ComparableFoo need not extend Foo. In some cases that might be nice, but not a requirement. If you really want to get at the underlying Foo, you have it in a field, and you could either access that field, or provide a formal accessor.

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