You need to be aware of this: A double is just a number. It doesn't have any inherent format.
When you want to print a number to the screen, it has to be converted to text (digits, '1', '7', '5', etc.). When you convert a number to text, you do this using a specified format.
The method parseDouble in class Double does the opposite: it parses text and converts it to a number. As I said above, once the text is converted to a number, it's just a number, and it doesn't have a format.
If you use println to print a double, you don't specify the format which is to be used to convert the number back to text, so println uses a default format, and your number comes out as "1.7514E7".
If you want to explicitly specify how the number should be formatted, you should use a class like java.text.DecimalFormat. For example: