Add objects to a mutable list in scala

Question

I've been trying to add data to a mutable list in scala.

I can add basic datatypes fine, thanks to Alvin Alexanders excellent blog post using a ListBuffer class, but when it comes to objects, Im not really sure how to proceed so please dont mark as duplicate just yet.

import scala.collection.mutable.ListBuffer

var fruits = new ListBuffer[String]()
fruits += "Apple"
fruits += "Banana"
fruits += "Orange"

So, I try to map this like so:

import scala.collection.mutable.ListBuffer
var fruits = new ListBuffer[MyClass]()
var d1=new MyClass("data1","data2","data3")

fruits += d1

This gives the following error:

type mismatch
found: MyClass
required: MyClass

Can anyone help me here?

This works for me in the REPL, can you add a more detailed description? — Ende Neu
– Ende Neu, Commented Aug 13, 2014 at 12:24

monnef · Accepted Answer · 2014-08-13 12:56:11Z

2

Unable to reproduce:

Welcome to Scala version 2.10.2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_25).
Type in expressions to have them evaluated.
Type :help for more information.

scala> :paste
// Entering paste mode (ctrl-D to finish)

import scala.collection.mutable.ListBuffer
var fruits = new ListBuffer[MyClass]()
class MyClass(a:String, b:String, c:String)
var d1=new MyClass("data1","data2","data3")
fruits += d1

// Exiting paste mode, now interpreting.

import scala.collection.mutable.ListBuffer
fruits: scala.collection.mutable.ListBuffer[MyClass] = ListBuffer(MyClass@291c57ba)
defined class MyClass
d1: MyClass = MyClass@291c57ba
res0: scala.collection.mutable.ListBuffer[MyClass] = ListBuffer(MyClass@291c57ba)

EDIT:
You might have re-defined MyClass and it led to "type mismatch" error. Maybe something like this:

scala> :paste
// Entering paste mode (ctrl-D to finish)

import scala.collection.mutable.ListBuffer
class MyClass(a:String, b:String, c:String)
var fruits = new ListBuffer[MyClass]()

// Exiting paste mode, now interpreting.

import scala.collection.mutable.ListBuffer
defined class MyClass
fruits: scala.collection.mutable.ListBuffer[MyClass] = ListBuffer()

scala> :paste
// Entering paste mode (ctrl-D to finish)

class MyClass(a:String, b:String, c:String)
var d1=new MyClass("data1","data2","data3")
fruits += d1

// Exiting paste mode, now interpreting.

<console>:14: error: type mismatch;
 found   : MyClass(in object $iw)(in object $iw)(in object $iw)(in object $iw)
 required: MyClass(in object $iw)(in object $iw)(in object $iw)(in object $iw)
              fruits += d1
                        ^

edited Aug 13, 2014 at 12:56

answered Aug 13, 2014 at 12:24

monnef

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5 Comments

Mkl Rjv Over a year ago

Here's the thing, Ive been trying each command one by one in scala terminal. Now, I tried the paste method and it works. Whats happening here?

monnef Over a year ago

I would guess you had an old instance of MyClass, then you redefined MyClass, created ListBuffer with new MyClass and tried pushing there an old instance of MyClass.

Mkl Rjv Over a year ago

I redefined MyClass each time. Doesnt that override the old one?

monnef Over a year ago

Yes it does override class definition, but not the already created instances of the old MyClass, answer updated.

Ajay Sant Over a year ago

Thanks for the :paste didn't know it was there to be used in REPL

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