java的四捨五入

import java.math.BigDecimal;

public class jamesMath {

private static final int DEF_DIV_SCALE = 10;

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();

}

/**

* 兩個Double數相加

* @param v1

* @param v2

* @return double

*/

public static double add(Double v1,Double v2){

BigDecimal b1 = new BigDecimal(v1.toString());

BigDecimal b2 = new BigDecimal(v2.toString());

return b1.add(b2).doubleValue();

}

/**

* 兩個Double數相減

* @param v1

* @param v2

* @return double

*/

public static double sub(Double v1,Double v2){

BigDecimal b1 = new BigDecimal(v1.toString());

BigDecimal b2 = new BigDecimal(v2.toString());

return b1.subtract(b2).doubleValue();

}

/**

* 兩個Double數相乘

* @param v1

* @param v2

* @return double

*/

public static double mul(Double v1,Double v2){

BigDecimal b1 = new BigDecimal(v1.toString());

BigDecimal b2 = new BigDecimal(v2.toString());

return b1.multiply(b2).doubleValue();

}

/**

* 兩個Double數相除

* @param v1

* @param v2

* @return double

*/

public static double div(Double v1,Double v2){

BigDecimal b1 = new BigDecimal(v1.toString());

BigDecimal b2 = new BigDecimal(v2.toString());

return b1.divide(b2,DEF_DIV_SCALE,BigDecimal.ROUND_HALF_UP).doubleValue();

}

/**

* 兩個Double數相除，並保留scale位小數

* @param v1

* @param v2

* @param scale

* @return double

*/

public static double div(Double v1,Double v2,int scale){

if(scale<0){

throw new IllegalArgumentException(

"The scale must be a positive integer or zero");

}

BigDecimal b1 = new BigDecimal(v1.toString());

BigDecimal b2 = new BigDecimal(v2.toString());

return b1.divide(b2,scale,BigDecimal.ROUND_HALF_UP).doubleValue();

}

}