这看起来更像人类的推理，因此更清晰（同时对计算机来说没有更高的成本）：

if a and b are 0
  if last price is also 0 price = previous close
  else price = last price
else if b is zero /* and therefore at this point a isn't */ price = a
else if a is zero /* and therefore b isn't */ price = b
else /*a and b are nonzero, so */ price = (b+a)/2

你可以使用streams来写：

price = DoubleStream.of(a, b)
    .filter(x -> x != 0)
    .average()
    .orElse(LastPrice != 0 ? LastPrice : previousClose)

下面是一个改进的if-else语句，它删除了一些重复检查。

if (b != 0. && a != 0.) {
  price = (b + a) / 2;
} else if (b == 0.) { //don't need to check a not equal to zero, because if so we would have been in the previous condition.
   price = a;
} else if (a == 0) { // same here
   price = b;
} else if (LastPrice != 0.) { // same here don't need to check that a and b are not null already checked that case on the first line
    price = LastPrice;
} else {
   price = previous close;
}

或者你可以做一些if语句的嵌套

if (b == 0. && a == 0. && LastPrice == 0.) {
    price = previous close;
  } else {
   if (b == 0.) { 
     price = a;
   } else if (a == 0) { 
     price = b;
   } else if { 
     price = LastPrice;
   }
}