在JAVA中，可以使用大十进制浮点数和双数减去

Question

Here is the Code(i am giving fraction of code) Below code is of withdraw of savings account:-

I have declared variables as below:-

protected static double balance;
protected static float amount;

So i opened account with balance as 7095, then i am performing withdraw operation, entering amount as 100.0. I am getting below results which is wrong. If i enter amount as 100, getting expecting results. Need help.

Total balance:- 7095
Withdraw amount:- 48
Current balance:- 7047

---

  BigDecimal amount3 = new BigDecimal(balance);
  BigDecimal amount4 = new BigDecimal(amount) ;
  System.out.println("Total balance" +amount3);
  System.out.println("Withdraw amount" + amount4);
  Object obj = new Object();
  obj = (amount3.subtract(amount4));
  System.out.println("Current balance" +obj);

Answer 1

Binary floating-point ( float and double in Java) can only represent fractional numbers of a form counter-intuitive to base-10-using humans. The number 0.1 is famously not representable in binary floating-point, for instance.

The problem with binary floating-point is not addition and subtraction. The problem is the representation of (some) fractional numbers of interest to you, in particular, decimal numbers. Therefore, it will not help to convert to BigDecimal numbers that are already represented in binary floating-point. They have already been approximated at the instant it was chosen to represent them as float and double . Computing as accurately as you want won't erase the representation error that was made then.

If you care about representing decimal numbers exactly, do not use binary floating-point to store them. In other words, do not declare amount and balance with binary floating-point types float and double .