Java: Java. Lang. Double Cannot Be Cast to Java. Lang. String

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 );
.
.
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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")));