1.代码：
import java.math.BigDecimal;
import java.text.DecimalFormat;
import java.text.NumberFormat;
public class format {
double f = 111231.5585;
public void m1() {
BigDecimal bg = new BigDecimal(f);
double f1 = bg.setScale(2, BigDecimal.ROUND_HALF_UP).doublevalue();
System.out.println(f1);
}
public void m2() {
DecimalFormat df = new DecimalFormat("#.00");
System.out.println(df.format(f));
}
public void m3() {
System.out.println(String.format("%.2f", f));
}
public void m4() {
NumberFormat nf = NumberFormat.getNumberInstance();
nf.setMaximumFractionDigits(2);
System.out.println(nf.format(f));
}
public static void main(String[] args) {
format f = new format();
f.m1();
f.m2();
f.m3();
f.m4();
}
}
2.输出结果:
111231.56
111231.56
111231.56
111,231.56
这里我们提供了一个工具类，定义浮点数的加、减、乘、除和四舍五入等运算方法。以供参考。
源文件MathExtend.java：
import java.math.BigDecimal;
public class MathExtend
{
//默认除法运算精度
private static final int DEFAULT_DIV_SCALE = 10;
public static double add(double v1, double v2)
{
BigDecimal b1 = new BigDecimal(Double.toString(v1));
BigDecimal b2 = new BigDecimal(Double.toString(v2));
return b1.add(b2).doublevalue();
}
public static String add(String v1, String v2)
{
BigDecimal b1 = new BigDecimal(v1);
BigDecimal b2 = new BigDecimal(v2);
return b1.add(b2).toString();
}
public static double subtract(double v1, double v2)
{
BigDecimal b1 = new BigDecimal(Double.toString(v1));
BigDecimal b2 = new BigDecimal(Double.toString(v2));
return b1.subtract(b2).doublevalue();
}
public static String subtract(String v1, String v2)
{
BigDecimal b1 = new BigDecimal(v1);
BigDecimal b2 = new BigDecimal(v2);
return b1.subtract(b2).toString();
}
public static double multiply(double v1, double v2)
{
BigDecimal b1 = new BigDecimal(Double.toString(v1));
BigDecimal b2 = new BigDecimal(Double.toString(v2));
return b1.multiply(b2).doublevalue();
}
public static String multiply(String v1, String v2)
{
BigDecimal b1 = new BigDecimal(v1);
BigDecimal b2 = new BigDecimal(v2);
return b1.multiply(b2).toString();
}
public static double divide(double v1, double v2)
{
return divide(v1, v2, DEFAULT_DIV_SCALE);
}
public static double divide(double v1,double v2, int scale)
{
return divide(v1, v2, scale, BigDecimal.ROUND_HALF_EVEN);
}
public static double divide(double v1,double v2,int scale, int round_mode){
if(scale < 0)
{
throw new IllegalArgumentException("The scale must be a positive integer or zero");
}
BigDecimal b1 = new BigDecimal(Double.toString(v1));
BigDecimal b2 = new BigDecimal(Double.toString(v2));
return b1.divide(b2, scale, round_mode).doublevalue();
}
public static String divide(String v1, String v2)
{
return divide(v1, v2, DEFAULT_DIV_SCALE);
}
public static String divide(String v1, String v2, int scale)
{
return divide(v1, v2, DEFAULT_DIV_SCALE, BigDecimal.ROUND_HALF_EVEN);
}
public static String divide(String v1, String v2, int scale, int round_mode)
{
if(scale < 0)
{
throw new IllegalArgumentException("The scale must be a positive integer or zero");
}
BigDecimal b1 = new BigDecimal(v1);
BigDecimal b2 = new BigDecimal(v2);
return b1.divide(b2, scale, round_mode).toString();
}
public static double round(double v,int scale)
{
return round(v, scale, BigDecimal.ROUND_HALF_EVEN);
}
public static double round(double v, int scale, int round_mode)
{
if(scale<0)
{
throw new IllegalArgumentException("The scale must be a positive integer or zero");
}
BigDecimal b = new BigDecimal(Double.toString(v));
return b.setScale(scale, round_mode).doublevalue();
}
public static String round(String v, int scale)
{
return round(v, scale, BigDecimal.ROUND_HALF_EVEN);
}
public static String round(String v, int scale, int round_mode)
{
if(scale<0)
{
throw new IllegalArgumentException("The scale must be a positive integer or zero");
}
BigDecimal b = new BigDecimal(v);
return b.setScale(scale, round_mode).toString();
}
}
