getGender（）使用isMale返回null

Question

Whenever I run the getGender() it shows as null . It's the isMale that confuses me.

public Student(String sid, String name,  boolean isMale)
{       
    this.sid = sid;
    this.name = name;
    this.isMale = isMale;
    courses = "30202";  // default is empty
}

I have made it be able to return a value but it returns it as "true" or "false" and doesn't return it as "Male" or "Female" but this is the code in which returns it as null. I'm at a standstill.

Answer 1

Your constructor doesn't set your field String gender . You could,

public Student(String sid, String name,  boolean isMale){       
  this.sid = sid;
  this.name = name;
  this.isMale = isMale;
  this.gender = (isMale) ? "Male" : "Female";
  courses = "30202";  // default is empty
}

Of course, then your output might be

Male: Female

So, I think you really wanted

// System.out.println("Male: " + getGender());
System.out.println("Gender: " + getGender());

Then you would get

Gender: Male

or

Gender: Female

Answer 2

Your isMale variable indicates whether the person isMale or not.

You should change the getGender method so that it will return "Male" when isMale == true and "Female" when isMale == false.

   /**
     * Get the gender of the student, i.e. "Male" or "Female"
     *
     * @return The String "Male" if the student is male,
     *         otherwise "Female".
     */
    public String getGender()
    {
        if(isMale) {
          gender = "Male";
        }
        else{
          gender = "Female";
        }
       return gender;
    }

Answer 3

There is nothing that sets the gender field in your class.

In general, you shouldn't have both an isMale variable and a gender variable. That's redundant. You can derive one from the other, and isMale is a better implementation because you have only two states (not trying to be anti-trans here, that's simply the basic assumption in most student assignment).