GLUT displayfunc is called at event without callbacksetting - c++

Question

i have a weird situation that display function is called at mouse or key pressed even i didn't set mouse callback or key callback also all variables are stayed constant but object is always moved whatever event is occurred
so there are two problems:
why display func is called at event even there is none of preset of callback func?
why my object or cam is moving even there are no change of variables?
float camX = 0, camY = 2, camZ = 20;
float camXdest = 0, camYdest = 0, camZdest = 0;
float camUpx = 0, camUpy = 1, camUpz = 0;
float JbaseOffest = -15;
float JoffestDegree[3] = { JbaseOffest,0,0 };
float JrotateAxis = 2, JrotateDegree = 0;
float Jsize = 1;
void Reshape(int width, int hieght) {
glViewport(0, 0, width, hieght);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
float ratio = width / hieght;
gluPerspective(40, ratio, 0, 50);
}
void Rotate(float degree, int axis) {
if (axis == 0)
glRotatef(degree, 1, 0, 0);
else if (axis == 1)
glRotatef(degree, 0, 1, 0);
else if (axis == 2)
glRotatef(degree, 0, 0, 1);
}
void DrawJ(float dx = 0, float dy = 0, float dz = 0, float rotateDegree = 0, float rotateAxis = 0, float sizeCoefficient = 1) {
glPushMatrix();
//draw head of J
float size = 0.5 * sizeCoefficient;
glTranslatef(dx, dy + size * 4, dz);
glTranslatef(-size * 3, 0, 0);
Rotate(rotateDegree, rotateAxis);
int i = 0;
for (; i < 6; i++) {
glutSolidCube(size);
glTranslatef(size, 0, 0);
}
//draw body of J
glTranslatef(-7 * size / 2, 0, 0);
i = 0;
for (; i < 6; i++) {
glutSolidCube(size);
glTranslatef(0, -size, 0);
}
glPopMatrix();
}
void Display() {
glClear(GL_COLOR_BUFFER_BIT);
gluLookAt(camX, camY, camZ, camXdest, camYdest, camZdest, camUpx, camUpy, camUpz);
DrawJ(JoffestDegree[0], JoffestDegree[1], JoffestDegree[2], JrotateDegree, JrotateAxis, Jsize);
//DrawS(SoffestDegree[0], SoffestDegree[1], SoffestDegree[2], SrotateDegree, SrotateAxis, Ssize);
//DrawM(MoffestDegree[0], MoffestDegree[1], MoffestDegree[2], MrotateDegree, MrotateAxis, Msize);
glutSwapBuffers();
}
int main(int argc, char** argv) {
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
glutInitWindowSize(WINDOW_WIDTH, WINDOW_HEIGHT);
glutCreateWindow("Main");
glutDisplayFunc(Display);
glutReshapeFunc(Reshape);
//glutKeyboardFunc(CallBackKeyEvent);
glutMainLoop();
}