added warning if send amount is not set

src/main/java/fucoin/gui/WalletGuiControlImpl.java

@@ -7,6 +7,7 @@ import javax.swing.*;
 import java.awt.*;
 import java.awt.event.*;
 import java.util.Enumeration;
+import java.text.NumberFormat;
 
 public class WalletGuiControlImpl implements WalletGuiControl {
 
@@ -22,7 +23,7 @@ public class WalletGuiControlImpl implements WalletGuiControl {
     private JLabel lblSendTo = new JLabel("Send to:");
     private JComboBox<String> txtSendTo = new JComboBox<>();
     private JLabel lblSendAmount = new JLabel("Amount:");
-    private JTextField txtSendAmount = new JTextField("");
+    private JTextField txtSendAmount = new JFormattedTextField(NumberFormat.getNumberInstance());
     private JButton btnSend = new JButton("Send");
     private JButton btnSearch = new JButton("Search");
     private JButton btnStore = new JButton("Store");
@@ -128,8 +129,13 @@ public class WalletGuiControlImpl implements WalletGuiControl {
         window.setVisible(true);
 
         btnSend.addActionListener(e -> {
+        	String sendAmount = txtSendAmount.getText();
+        	if(sendAmount.trim().equalsIgnoreCase("")) {
+        		JOptionPane.showMessageDialog(new JFrame("Warning"), "You need to type a number of coins to send.");
+        	} else {
         		wallet.send(txtSendTo.getSelectedItem().toString(),
-                    Integer.parseInt(txtSendAmount.getText()));
+        				Integer.parseInt(sendAmount));
+        	}
         });
 
         btnStore.addActionListener(e -> {