I have a array which I convert to string to use it as key in an hashmap.
How is it possible to convert a string like this [5.0, -1.0, 2.0] again to an array consisting of three double values?
PS: I'm kind of new to java but I couldnt find a solution here or via google.
It's possible, with a bit of fiddling - and by the way, it's a very, very bad idea to use an array as a key to a Map (even if it's converted to a String), because it can change its contents. Try this:
String array = "[5.0, -1.0, 2.0]";
String[] data = array.substring(1, array.length()-1).split(", ");
double[] answer = new double[data.length];
for (int i = 0; i < data.length; i++)
answer[i] = Double.parseDouble(data[i]);
Now answer will be an array of doubles with the values originally contained in the String.
There isn't any ready method for this. So, you have to create your own method, which will parse your string back into array of double-s. You can do it, using String.split(...) method for example.
See documentation for String.substring() and String.split().
Scanner sc = new Scanner(stringToParse);
ArrayList<Double> buffer = new ArrayList<>();
while(sc.hasNextDouble())
buffer.add(sc.nextDouble());
Object[] doubles = buffer.toArray();
Double[] doubles = buffer.toArray(new Double[buffer.size()])
Double[], OP was asking for a double[]Something like this might work
List<Double> yourDoubleList = new ArrayList<Double>();
String withoutBrackets = array.substring(1, array.length() - 1);
for(String number : withoutBrackets.split(",")) {
yourDoubleList.add(Double.parseDouble(number));
}
List<Double>, OP was asking for a double[]
List<Double>as the key in the hash map, rather than aString? Trying to dump it into aStringis definitely a code smell.