BigDecimal 遇到的坑
现象
public static void main(String[] args) {
BigDecimal one = new BigDecimal("60");
BigDecimal two = new BigDecimal("60.00");
System.out.println(one.equals(two));
System.out.println(one.doubleValue() == two.doubleValue());
System.out.println(one.setScale(2).equals(two.setScale(2)));
}
有一次编写了使用 equals() 进行两个金额值的比较，但是很不幸。
one.equals(two) 结果是 false。
解决方案可以是后面的两种方式。
个人比较倾向于第一种，直接获取对应的 double value。
equals 源码
/**
* Compares this {@code BigDecimal} with the specified
* {@code Object} for equality. Unlike {@link
* #compareTo(BigDecimal) compareTo}, this method considers two
* {@code BigDecimal} objects equal only if they are equal in
* value and scale (thus 2.0 is not equal to 2.00 when compared by
* this method).
*
* @param x {@code Object} to which this {@code BigDecimal} is
* to be compared.
* @return {@code true} if and only if the specified {@code Object} is a
* {@code BigDecimal} whose value and scale are equal to this
* {@code BigDecimal}'s.
* @see #compareTo(java.math.BigDecimal)
* @see #hashCode
*/
@Override
public boolean equals(Object x) {
if (!(x instanceof BigDecimal))
return false;
BigDecimal xDec = (BigDecimal) x;
if (x == this)
return true;
if (scale != xDec.scale)
return false;
long s = this.intCompact;
long xs = xDec.intCompact;
if (s != INFLATED) {
if (xs == INFLATED)
xs = compactValFor(xDec.intVal);
return xs == s;
} else if (xs != INFLATED)
return xs == compactValFor(this.intVal);
return this.inflated().equals(xDec.inflated());
}
可以发现，如果二者的精度不同，也是直接会返回 false 的。
compareTo 源码
/**
* Compares this {@code BigDecimal} with the specified
* {@code BigDecimal}. Two {@code BigDecimal} objects that are
* equal in value but have a different scale (like 2.0 and 2.00)
* are considered equal by this method. This method is provided
* in preference to individual methods for each of the six boolean
* comparison operators ({@literal <}, ==,
* {@literal >}, {@literal >=}, !=, {@literal <=}). The
* suggested idiom for performing these comparisons is:
* {@code (x.compareTo(y)} <<i>op</i>> {@code 0)}, where
* <<i>op</i>> is one of the six comparison operators.
*
* @param val {@code BigDecimal} to which this {@code BigDecimal} is
* to be compared.
* @return -1, 0, or 1 as this {@code BigDecimal} is numerically
* less than, equal to, or greater than {@code val}.
*/
public int compareTo(BigDecimal val) {
// Quick path for equal scale and non-inflated case.
if (scale == val.scale) {
long xs = intCompact;
long ys = val.intCompact;
if (xs != INFLATED && ys != INFLATED)
return xs != ys ? ((xs > ys) ? 1 : -1) : 0;
}
int xsign = this.signum();
int ysign = val.signum();
if (xsign != ysign)
return (xsign > ysign) ? 1 : -1;
if (xsign == 0)
return 0;
int cmp = compareMagnitude(val);
return (xsign > 0) ? cmp : -cmp;
}
doubleValue()
源码
/**
* Converts this {@code BigDecimal} to a {@code double}.
* This conversion is similar to the
* <i>narrowing primitive conversion</i> from {@code double} to
* {@code float} as defined in section 5.1.3 of
* <cite>The Java™ Language Specification</cite>:
* if this {@code BigDecimal} has too great a
* magnitude represent as a {@code double}, it will be
* converted to {@link Double#NEGATIVE_INFINITY} or {@link
* Double#POSITIVE_INFINITY} as appropriate. Note that even when
* the return value is finite, this conversion can lose
* information about the precision of the {@code BigDecimal}
* value.
*
* @return this {@code BigDecimal} converted to a {@code double}.
*/
public double doubleValue(){
if(intCompact != INFLATED) {
if (scale == 0) {
return (double)intCompact;
} else {
/*
* If both intCompact and the scale can be exactly
* represented as double values, perform a single
* double multiply or divide to compute the (properly
* rounded) result.
*/
if (Math.abs(intCompact) < 1L<<52 ) {
// Don't have too guard against
// Math.abs(MIN_VALUE) because of outer check
// against INFLATED.
if (scale > 0 && scale < double10pow.length) {
return (double)intCompact / double10pow[scale];
} else if (scale < 0 && scale > -double10pow.length) {
return (double)intCompact * double10pow[-scale];
}
}
}
}
// Somewhat inefficient, but guaranteed to work.
return Double.parseDouble(this.toString());
}
个人收获
使用一样东西之前，不能想当然的认为，最好是熟练的知道其中的原理。
不然，你会跳进神坑之中。
