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

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 ?

8 Answers

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.

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.

how about

mvalue = listMap.get("mvalue"); 

?

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> 

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.

try this :

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

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.

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