注意；float虽然是4个自减，但是它的取值范围却比8个字节的long要大。
float和double只能用来作科学计算或者是工程计算，但在商业计算中我们要用java.math.BigDecimal，通过使用BigDecimal类可以解决上述问题，实例代码如下：
package ex;
import java.math.*;
public class BigDecimalDemo {
public static void main(String[] args){
System.out.println(ArithUtil.add(0.01, 0.05));
System.out.println(ArithUtil.sub(1.0, 0.42));
System.out.println(ArithUtil.mul(4.015, 100));
System.out.println(ArithUtil.div(123.3, 100));
}
}class ArithUtil{
private static final int DEF_DIV_SCALE=10;
private ArithUtil(){}
//相加
public static double add(double d1,double d2){
BigDecimal b1=new BigDecimal(Double.toString(d1));
BigDecimal b2=new BigDecimal(Double.toString(d2));
return b1.add(b2).doubleValue();
}
//相减
public static double sub(double d1,double d2){
BigDecimal b1=new BigDecimal(Double.toString(d1));
BigDecimal b2=new BigDecimal(Double.toString(d2));
return b1.subtract(b2).doubleValue();
}
//相乘
public static double mul(double d1,double d2){
BigDecimal b1=new BigDecimal(Double.toString(d1));
BigDecimal b2=new BigDecimal(Double.toString(d2));
return b1.multiply(b2).doubleValue();
}
//相除
public static double div(double d1,double d2){
return div(d1,d2,DEF_DIV_SCALE);
}
public static double div(double d1,double d2,int scale){
if(scale<0){
throw new IllegalArgumentException("The scale must be a positive integer or zero");
}
BigDecimal b1=new BigDecimal(Double.toString(d1));
BigDecimal b2=new BigDecimal(Double.toString(d2));
return b1.divide(b2,scale,BigDecimal.ROUND_HALF_UP).doubleValue();
}
}