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equalsSystem.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 大于转载于:https://www.cnblogs.com/wwwcf1982603555/p/9051054.html
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