### [How to print formatted BigDecimal values?](https://stackoverflow.com/questions/3395825/how-to-print-formatted-bigdecimal-values)
千位數加逗號
```java
import java.math.BigDecimal;
import java.text.DecimalFormat;
```
```java
DecimalFormat df = new DecimalFormat("#,###");
System.out.println(df.format(new BigDecimal(7123456.75)));
// 7,123,457
```
```java
package poisondog.demo;
import java.math.BigDecimal;
/**
* @author Adam Huang
*/
public class DemoBigDecimal {
// 為需要四捨五入的數字，scale 為小數點後面要保留幾位數，return 四捨五入後的結果
public static double round(double v,int scale){
if(scale < 0){
throw new IllegalArgumentException("The scale must be a positive integer or zero");
}
BigDecimal b = new BigDecimal(Double.toString(v));
BigDecimal one = new BigDecimal("1");
return b.divide(one, scale, BigDecimal.ROUND_HALF_UP).doubleValue();
}
public static void main (String [] args) throws Exception {
BigDecimal bigNumber = new BigDecimal("89.1234567890123456789");
BigDecimal bigRate = new BigDecimal(1000);
BigDecimal bigResult = new BigDecimal(0);
// bigResult 為 bigNumBer * bigRate
bigResult = bigNumber.multiply(bigRate);
System.out.println(bigResult.toString()); // 89123.4567890123456789000
// 將 bigNumber 四捨五入變為 double 型態
double dData = bigNumber.doubleValue();
System.out.println(dData); // 89.12345678901235
// 宣告 data2 為 bigNumber/bigRate 並四捨五入至小數點第二位
double data2 = bigNumber.divide(bigRate, 2, BigDecimal.ROUND_HALF_UP) .doubleValue();
System.out.println(data2); // 0.09
}
}
```