Change Doubles to BigDecimals

Question

I Have this:

double priceMulti = 1.3;
double price = Double.parseDouble(jTextField1.getText());

//some if's and else's        

double date = (1980 * 2);
double random = Math.random()*15;
jLabel28.setText(String.valueOf((priceMulti * price * date * random)/price));
double copies = Double.parseDouble(jLabel28.getText());
jLabel33.setText(String.valueOf(copies / price));

code, and I want to change the variables of price and copies (whose are doubles) to BigDecimals. I Know that there are some topics like those, but my code is a bit different. Solved, thanks!

Answer 1

Change Doubles to BigDecimals

Look at the constructor BigDecimal(String)

    double val = 5.2;
    BigDecimal bd = new BigDecimal(String.valueOf(val));
    System.out.println(bd);

Explore other constructors also of BigDecimal.

Answer 2

The main thing to avoid is converting your strings to double at any point. Once you do that, the number is rounded to a binary fraction. You can, and should, construct a BigDecimal directly from a String that represents a decimal fraction.

import java.math.BigDecimal;

public class Test {
  public static void main(String[] args) {
    String s = "5.2";
    double d = 5.2;
    BigDecimal fromString = new BigDecimal(s);
    BigDecimal fromDouble = new BigDecimal(d);
    System.out.println("From string: " + fromString);
    System.out.println("From double: " + fromDouble);
  }
}

result:

From string: 5.2
From double: 5.20000000000000017763568394002504646778106689453125

fromString contains the exact conversion of "5.2" to a decimal fraction, ready to do arithmetic. fromDouble has first been rounded to a number that can be exactly represented as a binary fraction. It is very, very close to 5.2, but slightly different.

To construct a BigDecimal representing a compile-time constant, you still need to use the String argument constructor: new BigDecimal("5.2") not new BigDecimal(5.2).