java Double。最小值未按预期工作

Question

我有下面的代码，但当mutuaInformation为零时，它不会通过if。知道怎么回事吗

        int largestEntropyIndex = Integer.MIN_VALUE;
        double largestMutualInfomation = Double.MIN_VALUE;
        for (int i = 0; i < attributes.size(); i++) {
            String attrName=this.attributes.get(i);
            double conditionalEntropy = calcConditionalEntropy(i,
                                                               instances,
                                                               this.attributeValues.get(attrName).size(),
                                                               this.labels.size());

            System.out.println("conditional entropy is: "+conditionalEntropy);
            double mutualInformation = entropy - conditionalEntropy;
            if (mutualInformation > largestMutualInfomation){
                largestMutualInfomation = mutualInformation;
                largestEntropyIndex = i;
            }

Answer 1

执行简单的代码，你就会得到它

public static void main(String args[]) {
    System.out.println("Min value for Double : " + Double.MIN_VALUE);
    if(0 > Double.MIN_VALUE) {
        System.out.println("0 is greater than Double.MIN_VALUE");
    }
    else {
        System.out.println("0 is less than Double.MIN_VALUE");
    }
}

输出是

Min value for Double : 4.9E-324
0 is less than Double.MIN_VALUE

如您所见Double.MIN_VALUE的值大于0。因此你会注意到这种行为

Answer 2

常数Double.MIN_VALUE等于4.9E-324。虽然很小，但仍然大于绝对值0