Java使用HashMap用户输入循环

Question

I saw a student registration sample and wanted to write it using HashMap in my own way to learn more about HashMap .

About the program: 1)You can add student name and student id -class Student

import java.util.*;

public class Student {

    Scanner userInput = new Scanner(System.in);

    public String sName(){

        System.out.print("Enter student name: ");
        String sName = userInput.next();

        return sName;
    }

    public char sID(){
        System.out.print("Enter student ID: ");
        char sID= userInput.next().charAt(0);

        return sID;

    }

}

2)A class where I have declared 2 HashMap variables, one for student name and id and the second one for GPA and id -class AddInfo

import java.util.*;

public class AddInfo {

    public HashMap<String,Character> studentInfo= new HashMap<String,Character>();
    public HashMap<Double,Character> studentGPAInfo= new HashMap<Double,Character>();

}

3)You can add student GPA and student id – class StudentGPA

import java.util.*;

public class StudentGPA {

    Scanner userInput = new Scanner(System.in);

    public double sGPA(){

        System.out.print("Enter student GPA: ");
        double sGPA = userInput.nextDouble();

        return sGPA;
    }

    public char sID(){
        System.out.print("Enter student ID: ");
        char sID= userInput.next().charAt(0);

        return sID;

    }

}

4)The last one where all the information from the above classes are getting utilized using .put - class GetInfo

import java.util.*;

public class GetInfo {

    public HashMap<String,Double> myStudent=new HashMap<String,Double>();

    public void addName(){

        Student s= new Student();
        StudentGPA sG= new StudentGPA();


        AddInfo ai= new AddInfo();

        ai.studentInfo.put(s.sName(), s.sID());
        ai.studentGPAInfo.put(sG.sGPA(),sG.sID());


        if(s.sID()== sG.sID()){
            myStudent.put(s.sName(), sG.sGPA());

            System.out.println("For student id "+ s.sID()+ "you have " + myStudent); 
        }

    }

}

5)Main class

public class Main {

    public static void main (String []args){

        GetInfo g= new GetInfo();

        g.addName();

    }

}

My Problem: I think my issue is in the 4th point (GetInfo class) where I am trying to evaluate if the 2 student IDs are same or not. If they are same then put them in a different HashMap variable.

if(s.sID()== sG.sID())

When I execute the program it keeps on asking for Enter Student ID.

Any direction/advice will be helpful. Thank You for your valuable time and input.

Answer 1

Each time you do

if(s.sID()== sG.sID())

You are calling the sID() method of the class StudentGPA , which reads:

public char sID(){
    System.out.print("Enter student ID: ");
    char sID= userInput.next().charAt(0);

    return sID;

}

So of course you are being prompted for input.

You should write a setSid() that sets the value in a instance variable, and then a getSid() method that only returns the sID value without prompting for input.

Then you if statement will look like this:

if(s.getSid()== sG.getSid())

Answer 2

You have to one time init values and then use getter to get value

   public class StudentGPA {
        private double sGPA;
        private char sID;     
        Scanner userInput = new Scanner(System.in);


        public void initSGPA(){

            System.out.print("Enter student GPA: ");
            sGPA = userInput.nextDouble();
        }

        public  void initsID(){
            System.out.print("Enter student ID: ");
            sID= userInput.next().charAt(0);


        }

        public double getSGPA()
        {
           return sGPA;
        }
        public char getSID()
        {
           return sID;

        }
    }

In my opinion, the better way is using bean

   public class StudentGPA {
        private double sGPA;
        private char sID;     
        Scanner userInput = new Scanner(System.in);


        public void setSGPA(double sGPA){
            this.sGPA = sGPA;
        }

        public  void setSID(char sID){

            this.sID= sID;

        }

        public double getSGPA()
        {
           return sGPA;
        }
        public char getSID()
        {
           return sID;

        }
    }

..... move user intput into addName or separate procedure in GetInfo class

 ....
 System.out.print("Enter student GPA: ");
 sG.setSGPA(userInput.nextDouble());
 System.out.print("Enter student ID: ");
 sG.setSID(userInput.next().charAt(0));
 .....
 AddInfo ai= new AddInfo();

 ai.studentInfo.put(s.getSName(), s.getSID());
 ai.studentGPAInfo.put(sG.getSGPA(),sG.getSID());