Java正确比较浮点数的方法

double d1 = .1 * 3;
double d2 = .3;
System.out.println(d1 == d2);

final double THRESHOLD = .0001;

double d1 = .1 * 3;
double d2 = .3;

if(Math.abs(d1-d2) < THRESHOLD) {
	System.out.println("d1 和 d2 相等");
} else {
	System.out.println("d1 和 d2 不相等");
}

BigDecimal a = new BigDecimal("2.00");
BigDecimal b = new BigDecimal("2.0");

System.out.println(a.equals(b));
System.out.println(a.compareTo(b) == 0);

private int compareMagnitude(BigDecimal val) {
  // Match scales, avoid unnecessary inflation
  long ys = val.intCompact;
  long xs = this.intCompact;
  if (xs == 0)
    return (ys == 0) ? 0 : -1;
  if (ys == 0)
    return 1;

  long sdiff = (long)this.scale - val.scale;
  if (sdiff != 0) {
    // Avoid matching scales if the (adjusted) exponents differ
    long xae = (long)this.precision() - this.scale;  // [-1]
    long yae = (long)val.precision() - val.scale;   // [-1]
    if (xae < yae)
      return -1;
    if (xae > yae)
      return 1;
    if (sdiff < 0) {
      // The cases sdiff <= Integer.MIN_VALUE intentionally fall through.
      if ( sdiff > Integer.MIN_VALUE &&
          (xs == INFLATED ||
              (xs = longMultiplyPowerTen(xs, (int)-sdiff)) == INFLATED) &&
          ys == INFLATED) {
        BigInteger rb = bigMultiplyPowerTen((int)-sdiff);
        return rb.compareMagnitude(val.intVal);
      }
    } else { // sdiff > 0
      // The cases sdiff > Integer.MAX_VALUE intentionally fall through.
      if ( sdiff <= Integer.MAX_VALUE &&
          (ys == INFLATED ||
              (ys = longMultiplyPowerTen(ys, (int)sdiff)) == INFLATED) &&
          xs == INFLATED) {
        BigInteger rb = val.bigMultiplyPowerTen((int)sdiff);
        return this.intVal.compareMagnitude(rb);
      }
    }
  }
  if (xs != INFLATED)
    return (ys != INFLATED) ? longCompareMagnitude(xs, ys) : -1;
  else if (ys != INFLATED)
    return 1;
  else
    return this.intVal.compareMagnitude(val.intVal);
}

BigDecimal d1 = new BigDecimal("0.1");
BigDecimal three = new BigDecimal("3");
BigDecimal d2 = new BigDecimal("0.3");

d1 = d1.multiply(three);

System.out.println("d1 = " + d1);
System.out.println("d2 = " + d2);
System.out.println(d1.compareTo(d2));

d1 = 0.3
d2 = 0.3
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