CODEWITHSUNDEEP
listscala
Bitmap
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Reputation: 12538

Adding elements to global list object in scala

Allright guys, pardon me if this question has already been asked. Yet another Scala newbie question. So for example if I want to have a global List object which can be used as a place holder container, in Java I can easily do;

//share list object
private List<String> strList = new ArrayList<>();
void add(String el)
{
 strList.add(e);
}

static void main(String[] args) { 
{
  add("36 Chambers");
  out.println(strList.get(0));//assume only element
}

Similarly, if I simulate the same syntax in Scala - I end up with java.lang.IndexOutOfBoundsException: 0. How can one achieve similar with simple Scala?

  private var strList: List[String] = Nil
  def add(el: String) {
    strList :+ el
  }

  def main(args: Array[String]) {   
    add("36 Chambers")
    println(s(0)) //assume only element
  }

Upvotes: 2

Views: 1040

Answers (1)

flavian
flavian

Reputation: 28511

To strictly answer your question:

private var strList: List[String] = Nil
def add(el: String) {
       strList = el :: strList;
}

You are using the wrong operator. You need to use ::. And you need to update inline because a List is of immutable length.

I'm switching the el and strList because :: is right associative, which means the method comes from the object to the right of the :: operator.

Also, the :: operator will perform a prepend, which means your elements will be in reverse order.

You can either call reverse at the end(before usage etc) or if you want something semantically similar to a Java ArrayList perhaps consider a Scala ListBuffer, a mutable collection to which you can append.

import scala.collection.mutable.ListBuffer;
private var strList: ListBuffer[String] = Nil
def add(el: String) {
       strList += el;
}

Upvotes: 1

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