How to randomly assigned employees from the list to 4 different groups

I have an employee class and I need to randomly assigned employees to a different groups (total 4) I never used random class before any ideas how to implement it.

public class EmployeeTest {

    public static void main(String[] args) {
        Random random = new Random();
        int group_num = random.nextInt(30);
        int max =0;
        if(max > 4) {
            group_num = 1;
        ArrayList<Employee> emp = new ArrayList();

        //for(int cnt = 1; cnt<4; cnt++) {
            //if(emplo)

        emp.add(new Employee("Tom", "Technology", 56, 34, 46, 23));
        emp.add(new Employee("Nick", "Technology", 65, 33, 21, 23));
        emp.add(new Employee("Jerry", "Technology", 56, 34, 46, 23));
        emp.add(new Employee("Janet", "Technology", 56, 34, 46, 23));
        emp.add(new Employee("Chitra", "Trading", 12, 54, 46, 23));
        emp.add(new Employee("Sally", "Trading", 16, 64, 46, 23));
    for(Employee e : emp) {
//          Random random = new Random();
//          int group_num = random.nextInt(30);
//          int max =0;
//          if(max > 4) {
//              group_num = 1;

            }

            System.out.println("Employee | identifier: " + e.getUnicIdentifier() + ", department: " + e.getDepartment() + ", texh_exp: " +  e.getTech_exp() + " , trade_exp: " + e.getTrade_exp() +
                " , op_exp: " + e.getOp_exp() + ", shared_exp: " + e.getShared_exp() + ", group_num: " + group_num);
        }