Finalised the quantity selector.

src/main/java/temp.java

@@ -94,7 +94,7 @@ public class temp extends javax.swing.JFrame {
 
         quantLabelchange.setText("Selected quantity:");
 
-        quantBox.setModel(new javax.swing.DefaultComboBoxModel<>(new String[] { "1", "2", "3", "4", "5" }));
+        quantBox.setModel(new javax.swing.DefaultComboBoxModel<>(new String[] { "Select a value", "1", "2", "3", "4", "5" }));
         quantBox.addActionListener(new java.awt.event.ActionListener() {
             public void actionPerformed(java.awt.event.ActionEvent evt) {
                 quantBoxActionPerformed(evt);
@@ -306,7 +306,12 @@ public class temp extends javax.swing.JFrame {
     private void quantBoxActionPerformed(java.awt.event.ActionEvent evt) {                                         
         // TODO add your handling code here:
         findItem();
-        quant = Double.parseDouble(quantBox.getSelectedItem().toString()) /2;
+        if (quantBox.getSelectedItem().toString()=="Select a value"){
+            error.setText("Please select an quantity;");
+        } else {
+            quant = Double.parseDouble(quantBox.getSelectedItem().toString()) /2;
+        }
+        
         //find the slected item and convet it into a double
         quantLabelchange.setText("Selected quantity: "+(quant*2));
         //update the display to show the quanity of item