I'm trying to create an array to collect students, and a grades array for each student. My int count will increment with a while loop or something. The problem is my Students array gets an error. Is there an alternative method?
static int count = 0;
static int[] Grades = new int[count];
static String[] Students = new String[Grades[count];
You can create a Student class which contains name, age...etc and an Array/List of grades :
class Student {
String name;
String age;
//...
List<Integer> grades;
//Getters & Setters of course
}
You can add a method that grab a map of {name:grades}
This design will create lot many problems for you in future. If you really want to stick with array., Do consider two dimensional arrays.
A better and clean design will be to use maps as follows.
map<Student, List<Grades>> studentGrades= new Hashmap <Student, List<Grades>>() ;
How about:
Map<String, ArrayList<Integer>> map = new HashMap<String, ArrayList<Integer>>();
To add:
String student = "Bobby";
int mark = 85;
if (map.containsKey(student))
map.get(student).add(mark);
else
{
ArrayList<Integer> arr = new ArrayList<Integer>();
arr.add(mark);
map.put(student, arr);
}
To display:
System.out.println(map);
or:
for (Entry<String, ArrayList<Integer>> entry: map.entrySet())
System.out.println("Marks of " + entry.getKey() + " = " + entry.getValue());
To extend functionality to allow students to have more properties:
class Student
{
ArrayList<Integer> marks;
// ...
}
Declaration:
Map<String, Student> students = new HashMap<String, Student>();
You can have a two-dimentional array. something like an array of arrays, that each item holds an entire array:
int[][] students = new int[num_of_students][]
Then you can dinamically change the length of each array for each student:
for (int i = 0; i < num_of_stuent; i++)
students[i] = new int[i + 1]
Studentclass and then use aStudent[]or aList<Student>.Map<Student, Grade>countset to 0, you'll always have a zero-length array, which you can never index into.