Java : java.lang.Double cannot be cast to java.lang.String

Question

I am storing a double value inside the a HashMap as shown

HashMap listMap = new HashMap();

double mvalue =0.0;

listMap.put("mvalue",mvalue );

Now when i tried to retrieve that value , as shown

mvalue = Double.parseDouble((String) listMap.get("mvalue"));

i am getting an error as

java.lang.Double cannot be cast to java.lang.String

I am confused here ,

This is my actual HashMap and i am setting the values in it as shown

HashMap listMap = new HashMap();
double mvalue =0.0 ;
List<Bag> bagList = null; 
listMap.put("bagItems",bagList);
listMap.put("mvalue", mvalue);

Could anybody please tell me , how the structure of the HashMap should be ?

In addition to the answers to your question, you may also want to read the tutorial on generics. docs.oracle.com/javase/tutorial/java/generics/index.html — Dunes
– Dunes, Commented Mar 6, 2012 at 11:47

planetjones · Accepted Answer · 2012-03-06 11:43:21Z

8

You have put a Double in the Map. Don't cast to String first. This will work:

HashMap<String, Double> listMap = new HashMap<String, Double>();
mvalue = listMap.get("mvalue");

Your primitive double is being Autoboxed to a Double Object. Use Generics to avoid the need to cast, which is the <String, Double> part.

answered Mar 6, 2012 at 11:43

planetjones

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Comments

SSpoke · Accepted Answer · 2014-03-12 01:13:31Z

3

I guess your map will store many diferents types So I recomend <String, Object> generic

HashMap listMap = new HashMap<String, Object>();
double mvalue =0.0;
listMap.put("mvalue",mvalue );
.
.
.
String mValueString = Double.toString((Double) listMap.get("mvalue"));

This will get you the double object, cast it to Double, and the convert into string in new variable.

edited Mar 12, 2014 at 1:13

SSpoke

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answered Mar 6, 2012 at 12:02

TulioPa

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1 Comment

Adizbek Ergashev Over a year ago

Thanks. HashMap listMap = new HashMap<String, Object>(); really solved the problem.

Kent · Accepted Answer · 2012-03-06 11:43:59Z

1

how about

mvalue = listMap.get("mvalue");

?

answered Mar 6, 2012 at 11:43

Kent

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Comments

Ramandeep Singh · Accepted Answer · 2012-03-06 11:44:11Z

1

First of all, make a HashMap with Class Types defined , like : HashMap<String,Double>

Secondly , this should work :

mvalue = Double.parseDouble(Double.toString(listMap.get("mvalue")));

Although, best way is :

mvalue = listMap.get("mvalue");
// provided defined HashMap is HashMap<String,Double>

answered Mar 6, 2012 at 11:44

Ramandeep Singh

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4 Comments

Harry Joy Over a year ago

if map stores double value then why to parse it? Here you are doing 2 unnecessary parsing. first double to string and then again string to double.

claesv Over a year ago

Sure, it works, but why go through the trouble of converting back and forth between String and Double when the value is already a Double?

Ramandeep Singh Over a year ago

yeah i knw..And i modified my answer to suit its needs..but i wanted to tell @yyy i 777 , how to go about in this situation..!!

planetjones Over a year ago

The Map already holds a Double. If mvalue needs to be a primitive then unboxing will do it. Why on earth would you do the toString call, only to parse it as a Double ?

Johan Sjöberg · Accepted Answer · 2012-03-06 11:44:39Z

1

If you introduce generics you will immeditely discover the probblem

Map<String, Double> listMap = new HashMap<String, Double>();
Double mvalue = listMap.get("mvalue");

The reason is that your map does return a Double and not a String, hence the error message.

answered Mar 6, 2012 at 11:44

Johan Sjöberg

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Comments

Bastiflew · Accepted Answer · 2012-03-06 11:46:57Z

0

try this :

HashMap<String, Double> listMap = new HashMap<String, Double>();
Double mvalue = 0.0;
listMap.put("mvalue", mvalue);
mvalue = listMap.get("mvalue");

answered Mar 6, 2012 at 11:46

Bastiflew

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Comments

Sebastien Lorber · Accepted Answer · 2012-03-06 12:02:50Z

0

Your code should looks like:

Map<String,Double> listMap = new HashMap<String,Double>();
double mvalue = 0.0;
listMap.put("mvalue", mvalue );
mvalue = Double.parseDouble( String.valueOf(listMap.get("mvalue")) );

Notice that if you need to retrieve a wrapper and not a primitive type, you can use on wrapper classes XXX.valueOf() instead of XXX.parseXXX() which returns a primitive.

answered Mar 6, 2012 at 12:02

Sebastien Lorber

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Comments

Chan W Lee · Accepted Answer · 2016-05-18 09:27:52Z

0

mvalue = Double.parseDouble(String.valueOf(listMap.get("mvalue")));

answered May 18, 2016 at 9:27

Chan W Lee

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