Hello,
I think the problem is this:
you create a new StudentRecord but you don't assign the object to the
Student
public Student(String name, double mathG, double englisG, double scienceG,
int id){
StudentRecord st=new StudentRecord();
st.setName(name);
st.setMathGrade(mathG);
st.setEnglishGrade(englisG);
st.setScienceGrade(scienceG);
*this.studentRecord = st;*
this.studentID=id;
increaseStudentCount();
}
2010/4/2 Juan Antonio Fernandez <[email protected]>
> Hello,
>
> I´m trying to do the exercise of Lab 1014 and I´ve got a problem.
>
> Here is my code.
>
> ////////STUDENT CLASS///////
>
> public class Student {
> private StudentRecord studentRecord;
> private int studentID;
> private static int studentCount = 0;
>
> public Student(String name, double mathG, double englisG, double
> scienceG, int id){
> StudentRecord st=new StudentRecord();
> st.setName(name);
> st.setMathGrade(mathG);
> st.setEnglishGrade(englisG);
> st.setScienceGrade(scienceG);
> this.studentID=id;
> increaseStudentCount();
> }
>
>
> public StudentRecord getStudentRecord(){
> return this.studentRecord;
> }
>
>
> public int getstudentID(){
> return this.studentID;
> }
>
>
> public static int getStudentCount(){
> return studentCount;
> }
>
> public static void increaseStudentCount(){
> studentCount++;
> }
>
>
> /////MAIN CLASS//////
>
> public class Main {
> public static void main(String[] args){
> Student student1 = new Student("Juan",9,7,5,1);
> Student student2 = new Student("Maria",6,4,8,2);
> Student student3 = new Student("Luis",8,4,3,3);
>
> /**
> * Printing student details
> */
>
> System.out.println("Student ID: "+student1.getstudentID());
> System.out.println("Name: "+student1.getStudentRecord().getName());
> <------------ HERE IS THE ERROR
>
> System.out.println("Total number of students:
> "+Student.getStudentCount());
> }
> }
>
> When I compile the main class I receive the following error on the
> highlighted line.
>
> Student ID: 1
> Exception in thread "main" java.lang.NullPointerException
> at Main.main(Main.java:21)
> Java Result: 1
> BUILD SUCCESSFUL (total time: 0 seconds)
>
> I guess that the problem is that since I create a new studentRecord object
> inside the Student constructor when I try to access to that object it
> doesn´t exists anymore or something like that. As far as I understand the
> exercise I must create a Student object which creates a StudentRecord object
> and then print information about both objects. If I want to use proper
> encapsulation but I do not know how to do it.
>
> Could you help me?
>
> Regards
>
> JA
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