Java Gui Sum of Two Number

Question

I made a GUI which basically adds the numbers from the two textfield. The problem is, if I leave the other textfield blank and the other textfield has a number, the result textfield is not updating.

public class AdditionGui extends JFrame implements ActionListener { private TextField tf1 , tf2 , tf3; private Label sign, equalsign; private int sum = 0; AdditionGui(){ setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); setLayout(new FlowLayout()); tf1 = new TextField(5); add(tf1); tf1.addActionListener(this); sign = new Label("+"); add(sign); tf2 = new TextField(5); add(tf2); tf2.addActionListener(this); equalsign = new Label("="); add(equalsign); tf3 = new TextField(5); add(tf3); setTitle("Sum of two numbers"); setSize(220,120); setVisible(true); } public void actionPerformed(ActionEvent ae) { int val1 = Integer.parseInt(tf1.getText()); int val2 = Integer.parseInt(tf2.getText()); sum = val1 + val2; tf3.setText("" + sum); } }

Abra · Accepted Answer · 2020-04-30 18:43:13Z

A blank text field means its contents cannot be parsed to an Integer. In that case this line of your code will throw NumberFormatException (if tf1 is blank).

int val1 = Integer.parseInt(tf1.getText());

In your actionPerformed() method, check that getText() returns a number.
I suggest setting a blank text field to zero, for example:

String text1 = tf1.getText(); if (text1.length() == 0) { text1 = "0"; } int val1 = Integer.parseInt(text1); String text2 = tf2.getText(); if (text2.length() == 0) { text2 = "0"; } int val2 = Integer.parseInt(text2); int sum = val1 + val2; tf3.setText(Integer.toString(sum));

Now something for you to think about.
What happens if the user enters a non-digit into one of the text fields?

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