程序打印額外的 null 我似乎無法擺脫

Question

public class Student {
    
    private String courses = null;
    
    }
.....Some code here.......
    
    //Enroll in courses
    public void enroll() {
        //Get inside a loop and user hits Q
        do { 
            System.out.print("Enter Course to Enroll(Q to quit): ");
            Scanner in = new Scanner(System.in);
            String course = in.nextLine();
            if (!course.equals("Q")) {
                courses = courses + "\n " + course;
                tuitionBalance = tuitionBalance + costOfCourse;
            
            }
            else{ break; }      
        }while ( 1!= 0);

    }


......Some code here......
    
    //Show Status
    public String showInfo() {
        return "Name: " + firstName + " " + lastName + 
                "\nGrade level: " + gradeYear +
                "\nStudent ID: " + studentId +
                "\nCourses Enrolled:" + courses +
                "\nBalance: $" + tuitionBalance;
    }


}

一切似乎都運行得很好。 但是在注冊課程后打印了一個額外的 null，它像拇指酸痛一樣突出。 我怎么能擺脫它？ 我嘗試將字符串變量課程設置為 null 並且也沒有分配但似乎不會影響結果

Name: Frank Kuo
Grade level: 1
Student ID: 11001
Courses Enrolled:null
 Math101
Balance: $0

Answer 1

您可以替換private String courses = null; private String courses = ""; 擺脫null 。