从java中使用scala.collection.immutable.Set的示例 [英] example of using scala.collection.immutable.Set from java

问题描述

有谁熟悉Scala的人知道如何使用 scala.collection.immutable.Set 从Java？我可以模糊地读取scaladoc，但不知道如何从java调用像 - 这样的Scala方法（我假设我只需要在我的classpath中包含一些scala .jar文件...）

解决方案

Scala将这些特殊符号写成$ plus，$ minus等。您可以通过运行javap来反映scala.collection.immutable。哈希集

这样可以执行如下代码：

 设置= new HashSet< String>（）; 
 s。$ plus（one）; 
  

不漂亮，它在运行时实际上不起作用！你得到一个NoSuchMethodError。我猜这是与这个讨论。使用他们讨论的解决方法，您可以使工作：

  import scala.collection.generic.Addable; 
 import scala.collection.generic.Subtractable; 
 import scala.collection.immutable.HashSet; 
 import scala.collection.immutable.Set; 
 
 public class Test {
 public static void main（String [] args）{
 Set s = new HashSet< String>（）; 
 s =（Set< String>）（（Addable））$ plus（GAH！）; 
 s =（Set< String>）（（Addable）s）。$ plus（YIKES！）; 
 s =（Set< String>）（（Subtractable））$ minus（GAH！）; 
 System.out.println（s）; //打印Set（YIKES！）
} 
} 
  

不是那个美丽！

我相信Java 7将允许时髦的方法名称被转义，所以也许你可以做到这一点。

  s = s。＃ - （'GAH！'）
  

要尝试这样做，您需要Scala发行版的lib /文件夹中的scala-library.jar。

更新：修复Java 7语法，谢谢Mirko。

Does anyone out there who's familiar with Scala know how I could use scala.collection.immutable.Set from Java? I can vaguely read the scaladoc, but am not sure how to call scala methods like "-" from java (I assume that I just need to include some scala .jar file in my classpath...?)

解决方案

Scala writes those special symbols out as $plus, $minus, etc. You can see that for yourself by running javap against scala.collection.immutable.HashSet.

That allows you to do code like this:

Set s = new HashSet<String>();
s.$plus("one");

Not pretty, and it doesn't actually work at runtime! You get a NoSuchMethodError. I'm guessing it's related to this discussion. Using the workaround they discuss, you can get things working:

import scala.collection.generic.Addable;
import scala.collection.generic.Subtractable;
import scala.collection.immutable.HashSet;
import scala.collection.immutable.Set;

public class Test {
    public static void main(String[] args) {
        Set s = new HashSet<String>();
        s = (Set<String>) ((Addable) s).$plus("GAH!");
        s = (Set<String>) ((Addable) s).$plus("YIKES!");
        s = (Set<String>) ((Subtractable) s).$minus("GAH!");
        System.out.println(s); // prints Set(YIKES!)
    }
}

Isn't that a beauty!?

I believe Java 7 is going to allow funky method names to be escaped, so maybe by then you'll be able to do

s = s.#"-"('GAH!')

To try this, you need scala-library.jar from the lib/ folder of the Scala distribution.

Update: fixed Java 7 syntax, thanks Mirko.

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