getColumnName not working correctly

I am using a new class for a TableModel that extends AbstractTableModel, but when i try to add the header row it doesn't show. This is the code:

 public class StudentTableModel extends AbstractTableModel {

    private ArrayList<Student> student;
    private ArrayList<Group> groups;
    private int tableType=2;
    public String []coluNamess = {
                                    "id","name",
                                    "last name",
                                    " birth date",
                                    "phone","adress",
                                    "class"
                                 };
    public String  []coluNamesg = {
                                    "id","title",
                                    "level","num"
                                  };

    public String getColumnName(int column ) {
        if(tableType==1) {
            return this.coluNamess[column];
        } else {
            return this.coluNamesg[column];
        } 
    }

    public int getColumnCount() {
        if(tableType==1) {
            return 7;
        } else {
            return 4;
        }
    }

    public int getRowCount() {
        if(tableType==1) { 
            return student.size();
        } else {
            return groups.size();
        }
    }

    public String getValueAt(int row, int colu) {
        if(tableType==1) {
            Student studentm=student.get(row);
            switch(colu) {
                case 0:
                    return  Double.toString((double)studentm.getId());
                case 1:
                    return studentm.getFname();
                case 2:
                    return studentm.getLname();
                case 3:
                    return studentm.getB_date();
                case 4:
                    return studentm.getPhone();
                case 5:
                    return studentm.getAdress();
                case 6:
                    return Double.toString((double)studentm.getGroupId());
            }
        } else if(tableType==2) {
            Group group=groups.get(row);
            switch(colu) {
                case 0:
                    return  Double.toString((double)group.getId());
                case 1:
                    return  group.getTitle();
                case 2:
                    return  group.getLevel();
                case 3:
                    return  Double.toString((double)group.getTime());
            }
        }  
        return null;
    }

    public void setStudent(ArrayList<Student> students) {
        this.student= students;
    }

    public void setGroup(ArrayList<Group> groups) {
        this.groups= groups;
    }

    public void setType(int type) {
        this.tableType=type;
    }
}

The header is not appearing but the content is shown. I don't know where the problem is!!!!