Java APIs

I have this TXT file with some data that i read and insert it to an arraylist then i want to pass the data in to several variables but i keep getting an error when i convert it to double.

TXT file:
volvo
200000
0.7
2000
Mercedes
500000
1.0
1000
Fiat
100000
0.5
5000

Code:
class Register{
private ArrayList bilar = new ArrayList();
private BufferedReader indata = new BufferedReader(new InputStreamReader(System.in));

//Read the information from .txt"
public void läsInRegister() throws IOException{
try
{
FileReader file = new FileReader("C:/Users/Kelly/workspace/cla…
BufferedReader buf = new BufferedReader(file);
String in = buf.readLine();

while (in != null && !in.equals(""))
{
bilar.add(in);
in = buf.readLine();
}
System.out.println(bilar+ "\n" );
}
catch (Exception e){
}
}

public void set(){

for(int i=0; i< bilar.size(); i++) {

String str = bilar.get(i).toString();
String modell = str;
i=i++;
str="";
str = bilar.get(i).toString();
// until here everything is allright

// Now i have try with this ways but still nothing

double inköpspris = Double.parseDouble(str);
i=i++;
double bränsleförbrukning = (double) bilar.get(i);
i=i++;
double underhåll = (double) bilar.get(i);
i=i++;
double bränsleförbrukning = Double.parseDouble((String) bilar.get(i));
}
i can convert it to string there is no problem there, so i tried to convert the string str to double but still keeps getting the same error
the error is:

Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Double
at examples.Register.sortera(Bilkostnad.jav…
at examples.Bilkostnad.main(Bilkostnad.java…