变量bmr可能尚未初始化

Question

import java.util.Scanner; 

public class BMR 

{ 
public static void main(String[] args) 

{ 
    //object to use the keyboard input methods 

    Scanner in = new Scanner(System.in); 



    //ask the user to provide input 

    System.out.print("Enter your name: "); 

    String name = in.next(); 

    System.out.print("Gender (M of F): "); 

    String gender = in.next(); 

    System.out.print("Enter your age: "); 

    String age = in.next(); 

    System.out.print("Height in inches: "); 

    String height = in.next(); 

    System.out.println("Weight in pounds: "); 

    String weight = in.next(); 

    System.out.println(); 

    System.out.println(); 




    //convert measurements to metric units 

    double ageNum = Double.parseDouble(age); 

    double heightNum = Double.parseDouble(height); 

    double weightNum = Double.parseDouble(weight); 

    double heightCm = heightNum * 2.54; 

    double weightKilo = weightNum * 0.453592; 



    //calculate the BMR for males or females 

    double bmr; 

    if (gender == "M") 
     bmr = (13.397 * weightKilo) + (4.799 * heightCm) - (5.677 * ageNum) + 88.362; 

    else if (gender == "F") 
     bmr = (9.247 * weightKilo) + (3.098 * heightCm) - (4.330 * ageNum) + 447.593; 

    else 
     System.out.println("Please enter either M or F. I apologize for the gender binary."); 

    //display output 

    System.out.println("Calculate Your Basal Metabolism"); 

    System.out.println(); 

    System.out.println("Name: " + name); 

    System.out.println("Gender: " + gender); 

    System.out.println("Age: " + age); 

    System.out.println("Weight (kg): " + weightKilo); 

    System.out.println("Height (cm): " + heightCm); 

    System.out.println("Basal Metabolic Rate: " + bmr + " calories per day"); 





} 
} 

我必须为我的在线课程编写此代码来计算某人的基础代谢率。每次运行它时，我都会收到一个错误消息，说变量bmr可能没有被初始化。但我在条件语句中初始化了它。我究竟做错了什么？谢谢！

Answer 1

double bmr;变化double bmr=0;

你没有初始化局部变量。

你的代码还有一个错误。 gender是String，您正在比较String使用==这是错误的。你应该使用的

if (gender == "M") 

Answer 2

equals()

使用

if("M".equals(gender)) 

相反，你可以使用：

double bmr = 0.0; 

顺便说一句，你也应该使用：

"M".equals(gender) 

代替

gender == "M" 

这个错误发生，因为如果性别不是"M"或"F"，bmr不会当您使用它初始化。

Answer 3

Local variables and primitives should be initialized before use because you would know what to expect from the values. Historically, when a new variable was created it would contain random values from the memory [and one could not predict the value]. Java also requires this because it prevents the presence of orphaned variables.

变化

double bmr; 

到

double bmr=0; 

还可以使用

if("M".equals(gender)) 

，而不是

if (gender == "M") 

Answer 4

按Java的语法规则，方法的局部变量应该初始化。您尚未初始化您的本地变量。所以改变：

double bmr ; 

到

double bmr = 0.0; 

Answer 5

当你不初始化所有局部变量，会出现此错误。

你的情况，你必须做出如下修改：

double bmr = 0; 

Answer 6

你要的值设置为变量之前在所有情况下使用它。

在最后一个else中，bmr未初始化，但如果未输入性别，则可能不希望显示输出，因此，您可以在else中添加return子句以避免它。

else { 
     System.out.println("Please enter either M or F. I apologize for the gender binary."); 
     return; 
    } 

如果你想也显示输出在这种情况下，你必须提供一个valure到BMT：

else { 
     System.out.println("Please enter either M or F. I apologize for the gender binary."); 
     bmr = 0; 
    } 

Answer 7

double bmr; //initialization is not necessary here if we use following way around 

    if (gender == "M") 
    { 
     bmr = (13.397 * weightKilo) + (4.799 * heightCm) - (5.677 * ageNum) + 88.362; 
     System.out.println(bmr); //we are using bmr but after initialization in above line. So compiler doesn't complain. 
    } 

上面的代码是很确定，当您在使用左侧bmr=符号的一侧，您可以使用初始化后打印其值。在使用它之前，必须初始化变量。

但在以下情况下bmr在使用之前尚未初始化。

double bmr; 

    if (gender == "M") 
    { 
     System.out.println(bmr); //compiler complains here 
    } 

改正它初始化bmr为某个值，

double bmr=111; 

     if (gender == "M") 
     { 
      System.out.println(bmr); 
     } 

现在让我们从您的代码段检查不正确的代码。

double bmr; 
System.out.println("Basal Metabolic Rate: " + bmr + " calories per day"); //you have written this line next after 13 to 14 lines of code after `bmr` declaration where compiler complains for initialization;