[Java]ArrayIndexOutOfBoundsException

Sem pisal tudi na druge forume, pa upam da mi ne zamerate, ker sem pustil kar v Angleščini.

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {

String Temp = jComboBox1.getSelectedItem().toString();

testcomm.TestForm.WriteParamToPic("c"+Temp);

}



public static void WriteParamToPic(String ParamIn)
{
char [] WriteParam = new char[4];
byte [] FinalWriteParam = new byte[4];
WriteParam = ParamIn.toCharArray();
for(int i=0; i<4; i++){
FinalWriteParam[i] = (byte) WriteParam[i];
Comm.PutPointerData(FinalWriteParam,4);
}
}

I have:
jComboBox1.setModel(new javax.swing.DefaultComboBoxModel(new String[] {"30", "50" }));
i get nex error:
java.lang.ArrayIndexOutOfBoundsException


Hove must i configure argument for
WriteParamToPic
I have trayed to change number of arrays in WriteParamToPic, but it returns me other errors.

Thank you