Question

我正在关注Coursera的Scala课程，我已经实施了以下课程：

classdef Mesh

   properties
      nodes;    % its object will contain an object array of Node
      elements; % its object will contain an object array of Element
   end

   methods
     % Not interesting for this example
   end

end

但是，我收到很多编译错误。第一行出现在第一行：

 class Rational(x: Int, y: Int) {

  def numer = x;
  def denom = y;

  def add(that: Rational) = 
    new Rational(
        numer * that.denom + that.numer * denom,
        denom * that.denom)

  override def toString = numer + "/" + denom;

  def main(args: Array[String]){
    val x = new Rational(1, 2);
    x.numer;
    x.denom;
  }

}

包含代码的文件称为

Multiple markers at this line:

self constructor arguments cannot reference unconstructed this
constructor Rational#97120 is defined twice conflicting symbols both originated in file '/Users/octavian/workspace/lecture2/src/ex3.sc'
x is already defined as value x#97118
y is already defined as value y#97119

为什么会出现此错误？

Answer 1

您的main方法必须住在随附的object

中

class Rational(x: Int, y: Int) {

  def numer = x;
  def denom = y;

  def add(that: Rational) =
    new Rational(
      numer * that.denom + that.numer * denom,
      denom * that.denom)

  override def toString = numer + "/" + denom;
}

object Rational {
  def main(args: Array[String]) : Unit = {
    val x = new Rational(1, 2);
    x.numer;
    x.denom;
  }
}

我还更改了主方法签名，因为它可以防止错误指定显式返回类型并使用＆＃34; =＆＃34;。根据经验：永远不要忽略＆＃34; =＆＃34;登录

def main(args: Array[String]) : Unit = {

而不是

def main(args: Array[String]) {

Answer 2

我在eclipse scala-ide工作表（.sc文件）中定义一个类时遇到错误消息self constructor arguments cannot reference unconstructed this，并给它提供相同的类名（偶然），因为我命名为工作表外的类定义。删除重复的班级名称会让错误消失。

定义类时出现Scala错误

2 个答案: