[英]Extending Java Class with Scala Trait
I would like to define a class ContextItem
as the extension of java class Predicate
with a trait Confidence
. 我想将一个类ContextItem
定义为具有特征Confidence
度的java类Predicate
的扩展。
Confidence is a simple trait which simply adds a confidence field to whatever it extends. 信心是一个简单的特征,它只是为其扩展的内容添加一个置信区域。
trait Confidence{
def confidence:Double
}
I am defining my ContextItem
class by simply stating: 我只是通过声明来定义我的ContextItem
类:
class ContextItem extends Predicate with Confidence{}
But attempting to compile this yields... 但是试图编译它会产生......
com/slug/berds/Berds.scala:11: error: overloaded method constructor Predicate with alternatives:
(java.lang.String,<repeated...>[java.lang.String])com.Predicate <and>
(java.lang.String,<repeated...>[com.Symbol])com.Predicate <and>
(java.lang.String,java.util.ArrayList[com.Symbol])com.Predicate <and>
(com.Predicate)com.Predicate <and>
(com.Term)com.Predicate <and>
(java.lang.String)com.Predicate
cannot be applied to ()
class ContextItem(pred:Predicate) extends Predicate with Confidence{
^
This seems like a trivial example, so what's going wrong? 这似乎是一个微不足道的例子,所以出了什么问题?
Predicate (which is not mine) looks like: 谓词(不是我的)看起来像:
/** Representation of predicate logical form. */
public class Predicate extends Term implements Serializable {
public Predicate(String n) {
super(n);
}
public Predicate(Term t) {
super(t);
}
public Predicate(Predicate p) {
super((Term)p);
}
public Predicate(String n, ArrayList<Symbol> a) {
super(n, a);
}
public Predicate(String n, Symbol... a) {
super(n, a);
}
public Predicate(String n, String... a) {
super(n, a);
}
@Override
public Predicate copy() {
return new Predicate(this);
}
}
Neither Predicate nor any of its ancestors implements confidence. 谓词或其任何祖先都没有实现信心。
I think it is listing all the constructors of Predicate
, and informing you that you're not using any of them. 我认为它列出了Predicate
所有构造函数,并通知您没有使用它们中的任何一个。 The default is to use a parameterless constructor, which doesn't exist here. 默认设置是使用无参数构造函数,此处不存在。 The syntax to call, for example, the (String)
super-constructor, would be 调用的语法,例如, (String)
超级构造函数,将是
class ContextItem extends Predicate("something") with Confidence
or 要么
class ContextItem(str: String) extends Predicate(str) with Confidence
Also, at the moment your def confidence
is an abstract method, so won't compile until you give it a definition. 此外,目前你的def confidence
是一个抽象方法,所以在你给它定义之前不会编译。 If you intended the trait to add a writable confidence
field then this is what you want instead: 如果您希望该特征添加可写的confidence
区域,那么这就是您想要的:
var confidence: Double = 0.0
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.