Please, help me.i can't find what is error in my program in NETBEANS IDE

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Java

JavaSE

JavaSE6

netbeans

public class JavaApplication19 {

    public static void main(String[] args) {
        Lesson A = new Lesson();
        Lesson B = new Lesson();
        Lesson C = new Lesson();
        Lesson D = new Lesson("CMS 202", "Applied Linear Algebra", 3, 94);
        A.setCode("CMS 205");
        B.setCode("CMS 220");
        C.setCode("GERM 201");
        A.setName("Object Oriented Programming");
        B.setName("Web Programming 1");
        C.setName("German Language 1");
        A.setNote(99);
        B.setNote(97);
        C.setNote(95);
        A.setCredit(3);
        B.setCredit(3);
        C.setCredit(3);
        Student s = new Student("Nazli Elizade");
       System.out.println("Nazli's GPA is" + s.getGPA());
             System.out.println("Nazli's GPA is" +s.getTotalcredit());
    }

}

package javaapplication19;


public class Student {

    private String name;
    private Lesson listLesson[];
    private int size = 20;
    private int number = 0;

    public Student(String name) {
        this.name = name;
        listLesson = new Lesson[size];
    }

    public void addLesson(Lesson l) {
        if (number == size)
        {
            Lesson ListNew[] = new Lesson[size + 1];
            for (int i = 0; i < size; i++) {
                ListNew[i] = listLesson[i];
            }
            listLesson = ListNew;
            size++;
        }

    }

    public double getTotalcredit() {
        double t1;
        double total = 0;
        for (int i = 0; i < number; i++) {
            if (k.getNote() > 60) {
                t1 = k.getNote() * k.getCredit();
                total += t1;
            }

        }
        return total;
    }

    public double getGPA() {
        double GPA = 0.0;
        double t1;
        double total = 0.0;
        double totalcredit=1;
        for (int i = 0; i < number; i++) {
            if (k.getNote() > 60) {
                t1 = k.getNote() * k.getCredit();
                totalcredit += k.getCredit();
                total += t1;
            }
            GPA = total / (totalcredit-1);
            return GPA;
        }

public class Lesson {

    private String code;
    private String name;
    private double note;
    private int credit;

    public Lesson() {
        this.code = null;
        this.name = null;
        this.note = 0.0;
        this.credit = 0;
    }

    public Lesson(String c, String n, double note, int cre) {
        this.code = c;
        this.name = n;
        this.note = note;
        this.credit = cre;
    }

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getNote() {
        return note;
    }

    public void setNote(double note) {
        this.note = note;
    }

    public int getCredit() {
        return credit;
    }

    public void setCredit(int credit) {
        this.credit = credit;
    }

    public String toString() {
        return ("code=" + code + " " + "name=" + name + " " + "note=" + note + " " + "credit=" + credit);
    }

}

What I have tried:

There is no any error in this program,but when i run it ,error appears and it is like this:

Exception in thread "main" java.lang.RuntimeException: Uncompilable source code - missing return statement
	at javaapplication19.Student.getGPA(Student.java:52)
	at javaapplication19.JavaApplication19.main(JavaApplication19.java:32)
C:\Users\User\AppData\Local\NetBeans\Cache\8.1\executor-snippets\run.xml:53: Java returned: 1
BUILD FAILED (total time: 1 second)

When i click what this error points,i am reached to getGPA function.but please,help me what is problem in my program?
i wan to get student's GPA with this program.
I have searched about it,but i can't solve it.