Students tempStudent = new Students();
ændre det til
Students tempStudent;
Du overridding property of same object siden du oprettede tempStudent outside while loop . Du skal tilføje objects lig med number of record i databasen. Så opret tempStudent object som nedenfor.
brug
while (rs.next()) {
tempStudent = new Students();
tempStudent.studentId = rs.getInt("StudentNo");
tempStudent.studentName = rs.getString("StudentName");
tempStudent.studentAge = rs.getInt("StudentAge");
students.add(tempStudent);
size++;
}