为何我的Java程序计算BMI始终返回Infinity？求排查逻辑错误

我的程序通过BMI()方法计算患者的BMI，但无论输入什么合规值，返回结果都是Infinity。我知道数值除以0会返回Infinity，但已经对输入值做了非0限制，求帮忙找出逻辑错误。

原代码 #

import java.util.*;
public class PDProjectOne {
    private static double weight, age, biximent, genFactor, bmi;
    private static String gender;
    
    public static double genderFactor(){
        if(gender.equals("R") || (gender.equals("r"))){
            genFactor = 8.46;
        }
        if(gender.equals("S") || (gender.equals("s"))){
            genFactor = 4.23;
        }
        if(gender.equals("T") || (gender.equals("t"))){
            genFactor = 6.35;
        }
        return genFactor;
    }
    
    public static double BMI(){
        bmi = 2.56 * age + ((biximent * 467)/(weight * genFactor));
        return bmi;
    }
    
    public static void report(){
        Scanner sc = new Scanner(System.in);
        boolean good = false;
        do{
           System.out.print("Weight in kilograms:  ");
           weight = sc.nextDouble(); 
           if (weight <= 28){
               System.out.println("!! You must only enter a number greater than 28 kilograms. Try again. !!");
           }
           else{
            good = true;
        }
        } while (!good);
        
        good = false;
        do{
            System.out.print("Age in solar cycles:  ");
            age = sc.nextDouble();
            if (age >= 16 && age <= 96){
                good = true;
            }
            else{
                System.out.println("!! You must only enter an age between 16 and 96 solar cycles. Try again. !!");
            }
        } while (!good);
        
        good = false;
        do{
            System.out.print("Gender identification:  ");
            gender = sc.next();
            if (gender.equals("R") || gender.equals("r") || gender.equals("S") || gender.equals("s") || 
                    gender.equals("T") || gender.equals("t")){
                good = true;
            }
            else{
                System.out.println("!! You must only enter 'R','S',or 'T' as gender identifications. Try again. !!");
            }
        } while (!good);
        
        good = false;
        do{
            System.out.print("Biximent level:  ");
            biximent = sc.nextDouble();
            if (biximent >= 30){
                good = true;
            }
            else{
                System.out.println("!! You must only enter a biximent level of at least 30. Try again. !!");
            }
        } while (!good);
        
        System.out.println("\nSUMMARY OF ANALYSIS:\n"
                + "For a citizen of gender type " + gender + ", who is " + age + " cycles old and weighs " + weight + " kilograms with"
                        + " a reported Biximent Level of " + biximent + ", the Biximent Metabolic Index (BMI) is " + BMI());
    }
}

问题根源 #

你定义了genderFactor()方法来计算genFactor，但从来没有调用过这个方法！

静态变量genFactor的默认初始值是0.0，所以在BMI()方法里的weight * genFactor其实是weight * 0，结果必然是0，导致后面的除法(biximent * 467) / 0直接返回Infinity。

你的输入校验只限制了weight、age、biximent的取值，但没处理genFactor未初始化的问题。

修复方案 #

方案1：在调用BMI()前手动触发genderFactor() #

在report()方法的最后，调用BMI()之前，加一行调用genderFactor()的代码：

// 在打印摘要前先初始化genFactor
genderFactor();
System.out.println("\nSUMMARY OF ANALYSIS:\n"
        + "For a citizen of gender type " + gender + ", who is " + age + " cycles old and weighs " + weight + " kilograms with"
                + " a reported Biximent Level of " + biximent + ", the Biximent Metabolic Index (BMI) is " + BMI());

方案2：修改BMI()方法，直接在内部获取genFactor #

避免依赖静态变量的初始化，直接在BMI()里调用genderFactor()拿到值：

public static double BMI(){
    double factor = genderFactor();
    bmi = 2.56 * age + ((biximent * 467)/(weight * factor));
    return bmi;
}

额外优化建议 #

• 把genderFactor()里的多个if改成else if，减少不必要的判断：

public static double genderFactor(){
    if(gender.equalsIgnoreCase("R")){
        genFactor = 8.46;
    } else if(gender.equalsIgnoreCase("S")){
        genFactor = 4.23;
    } else if(gender.equalsIgnoreCase("T")){
        genFactor = 6.35;
    }
    return genFactor;
}

• 尽量避免使用过多静态变量，改成局部变量传递参数更安全，减少此类初始化问题。

内容的提问来源于stack exchange，提问作者PatPatis