一、BigDecimal构造方法（将其他类型转换成BigDecimal）；
1、 public BigDecimal(char[] in) {
this(in, 0, in.length);
}
2、 public BigDecimal(String val) {
this(val.toCharArray(), 0, val.length());
}
3、 public BigDecimal(String val, MathContext mc) {
this(val.toCharArray(), 0, val.length(), mc);
}
4、 public BigDecimal(double val) {
this(val,MathContext.UNLIMITED);
}
5、 public BigDecimal(BigInteger val) {
scale = 0;
intVal = val;
intCompact = compactValFor(val);
}
6、 public BigDecimal(int val) {
this.intCompact = val;
this.scale = 0;
this.intVal = null;
}
7、 public BigDecimal(long val) {
this.intCompact = val;
this.intVal = (val == INFLATED) ? INFLATED_BIGINT : null;
this.scale = 0;
}
利用其构造方法客将不同类型的数字转换成BigDecimal类型的数字；
二、利用BigDecimal实现加法（加法的方法）
public BigDecimal add(BigDecimal augend) {
if (this.intCompact != INFLATED) {
if ((augend.intCompact != INFLATED)) {
return add(this.intCompact, this.scale, augend.intCompact, augend.scale);
} else {
return add(this.intCompact, this.scale, augend.intVal, augend.scale);
}
} else {
if ((augend.intCompact != INFLATED)) {
return add(augend.intCompact, augend.scale, this.intVal, this.scale);
} else {
return add(this.intVal, this.scale, augend.intVal, augend.scale);
}
}
}
三、利用BegDecimal实现减法（减法的方法）
public BigDecimal subtract(BigDecimal subtrahend) {
if (this.intCompact != INFLATED) {
if ((subtrahend.intCompact != INFLATED)) {
return add(this.intCompact, this.scale, -subtrahend.intCompact, subtrahend.scale);
} else {
return add(this.intCompact, this.scale, subtrahend.intVal.negate(), subtrahend.scale);
}
} else {
if ((subtrahend.intCompact != INFLATED)) {
// Pair of subtrahend values given before pair of
// values from this BigDecimal to avoid need for
// method overloading on the specialized add method
return add(-subtrahend.intCompact, subtrahend.scale, this.intVal, this.scale);
} else {
return add(this.intVal, this.scale, subtrahend.intVal.negate(), subtrahend.scale);
}
}
}
四、利用BigDecimal实现乘法（乘法方法）
public BigDecimal multiply(BigDecimal multiplicand) {
int productScale = checkScale((long) scale + multiplicand.scale);
if (this.intCompact != INFLATED) {
if ((multiplicand.intCompact != INFLATED)) {
return multiply(this.intCompact, multiplicand.intCompact, productScale);
} else {
return multiply(this.intCompact, multiplicand.intVal, productScale);
}
} else {
if ((multiplicand.intCompact != INFLATED)) {
return multiply(multiplicand.intCompact, this.intVal, productScale);
} else {
return multiply(this.intVal, multiplicand.intVal, productScale);
}
}
}
五、利用BigDecimal实现处罚（出发方法）
public BigDecimal divide(BigDecimal divisor) {
/*
* Handle zero cases first.
*/
if (divisor.signum() == 0) { // x/0
if (this.signum() == 0) // 0/0
throw new ArithmeticException("Division undefined"); // NaN
throw new ArithmeticException("Division by zero");
}
// Calculate preferred scale
int preferredScale = saturateLong((long) this.scale - divisor.scale);
if (this.signum() == 0) // 0/y
return zeroValueOf(preferredScale);
else {
/*
* If the quotient this/divisor has a terminating decimal
* expansion, the expansion can have no more than
* (a.precision() + ceil(10*b.precision)/3) digits.
* Therefore, create a MathContext object with this
* precision and do a divide with the UNNECESSARY rounding
* mode.
*/
MathContext mc = new MathContext( (int)Math.min(this.precision() +
(long)Math.ceil(10.0*divisor.precision()/3.0),
Integer.MAX_VALUE),
RoundingMode.UNNECESSARY);
BigDecimal quotient;
try {
quotient = this.divide(divisor, mc);
} catch (ArithmeticException e) {
throw new ArithmeticException("Non-terminating decimal expansion; " +
"no exact representable decimal result.");
}
int quotientScale = quotient.scale();
// divide(BigDecimal, mc) tries to adjust the quotient to
// the desired one by removing trailing zeros; since the
// exact divide method does not have an explicit digit
// limit, we can add zeros too.
if (preferredScale > quotientScale)
return quotient.setScale(preferredScale, ROUND_UNNECESSARY);
return quotient;
}
}
以上为BigDecimal单参实现加减乘除的源码-------------------
六、用例子实现加减乘除
- /**
- * 提供精确的加法运算。
- * @param v1 被加数
- * @param v2 加数
- * @return 两个参数的和
- */
- 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();
- }
- /**
- * 提供精确的减法运算。
- * @param v1 被减数
- * @param v2 减数
- * @return 两个参数的差
- */
- public static double sub(double v1,double v2){
- BigDecimal b1 = new BigDecimal(Double.toString(v1));
- BigDecimal b2 = new BigDecimal(Double.toString(v2));
- return b1.subtract(b2).doubleValue();
- }
- /**
- * 提供精确的乘法运算。
- * @param v1 被乘数
- * @param v2 乘数
- * @return 两个参数的积
- */
- public static double mul(double v1,double v2){
- BigDecimal b1 = new BigDecimal(Double.toString(v1));
- BigDecimal b2 = new BigDecimal(Double.toString(v2));
- return b1.multiply(b2).doubleValue();
- }
- /**
- * 提供（相对）精确的除法运算，当发生除不尽的情况时，精确到
- * 小数点以后10位，以后的数字四舍五入。
- * @param v1 被除数
- * @param v2 除数
- * @return 两个参数的商
- */
- public static double div(double v1,double v2){
- return div(v1,v2,DEF_DIV_SCALE);
- }
- /**
- * 提供（相对）精确的除法运算。当发生除不尽的情况时，由scale参数指
- * 定精度，以后的数字四舍五入。
- * @param v1 被除数
- * @param v2 除数
- * @param scale 表示表示需要精确到小数点以后几位。
- * @return 两个参数的商
- */
- 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(Double.toString(v1));
- BigDecimal b2 = new BigDecimal(Double.toString(v2));
- return b1.divide(b2,scale,BigDecimal.ROUND_HALF_UP).doubleValue();
- }
***BigDecimal中的compareTo方法
BigDecimal a = new BigDecimal("1.00");
BigDecmial b = new BigDecimal(1);
想比较一下a和b的大小，一般都会用equals
System.out.println(a.equals(b));
但是输出结果是：false
原因是：BigDecimal比较时，不仅比较值，而且还比较精度？
if(a.compareTo(b)==0) 结果是true
比较大小可以用 a.compareTo(b)
返回值 -1 小于 0 等于 1 大于