Strange error to be solved - for he who knows

Question

Hi,
Below are the part are the codes presented that cause the problem. What happens is very strange to me and i would really appreciate it if someone could help me understand and solve the problem. If the excel file only contains numbers only or strings only in its columns the program works fine. but if the columns contains some string cells and some numbers then null is obtained for inputEx and otuputEx.
help needed!
conn_excel =DriverManager.getConnection(testcaseexcelodbc);        //conn_excel- connection to excel
Statement stmtExcel = conn_excel.createStatement();
ResultSet rsExcel = stmtExcel.executeQuery("Select Input, Output from [Sheet1$]");
while (rsExcel.next())
       String inputEx = rsExcel.getString("Input");
       String outputEx = rsExcel.getString("Output");
       System.out.println(intputEx);
       System.out.println(outputEx);
}                                        

Answer 1

Now this is very strange to me. assistance needed.
Below is what i tried
Test 1 - Excel File Columns
Input          output
1          1
2          2
3          3
4          4
Test1 Result: ok
Test 2 - Excel File Columns
Input          output
a          a
b          b
c          c
d          d
Test2 Result: ok
Test 3 - Excel File Columns
Input          output
1          1
2          2
c          c
4          4
Test3 Result: exception thrown on reading the cell where the number changes to string i.e. "c"
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