I have been learning Java for 3 months. I am doing Spring in training, but if the data type is Number I used Big Decimal instead of int for things that are only integers. Speaking of numbers, I used only ints or doubles, and I was confused about the processing of BigDecimal. There are many articles that are well organized about BigDecimal, I will summarize only the ones I actually used as a memorandum.
The four arithmetic operations are not "+", "-", "*", or "/".
| Calculation | Method | Example |
|---|---|---|
| Addition (A+ B） | add | A.add(B) |
| Subtraction (A- B） | subtract | A.subtract(B) |
| Multiplication (A* B） | multiply | A.multiply(B) |
| Gradual calculation (A/ B） | divide | A.divide(B) |
I haven't used gradual calculation, but if it's a decimal number, I need three arguments. A.divide (B, number of digits after the decimal point, rounding method (rounding up, rounding down, rounding, etc.)) I haven't used it this time, so I'll omit it.
Use "compareTo".
| Comparison operator | Return value | Example |
|---|---|---|
| A < B | If A is less than B-Returns 1 | A.compareTo(B) < 0 |
| A > B | Returns 1 if A is greater than B | A.compareTo(B) > 0 |
| A == B | Returns 0 if A and B are equal | A.compareTo(B) == 0 |
When I looked it up in the training, I wanted to make it "less than (<=") instead of "smaller (<)", so I wrote it like this.
//Not "greater than" (it will mess up your head)
if (!(A.compareTo(B) == 1)) {
}
//I think this was good
if (A.compareTo(B) <= 0) {
}
Since I also received the input value in String type and converted it to BigDecimal for processing, I will describe it.
BigDecimal→String
String String type variable name=Big Decimal type.toString();
String→BigDecimal
BigDecimal BigDecimal type variable name= new BigDecimal(String type);
https://docs.oracle.com/javase/jp/11/docs/api/java.base/java/math/BigDecimal.html https://www.sejuku.net/blog/25564 https://techacademy.jp/magazine/31915