How to read from user's input in Java and write it to a file

Question

I want to create a simple stand-alone application that will take some input from user (some numbers and mathematical functions f(x,y...)) and write them to a file. Then with

Answer 1

For your second question, you may like to consider having a JTextField on your JFrame for the user to enter lines into instead of a JOptionPane. It's just a simple text box, and you can add the box's contents to the file every time the button is pressed:

public static void main(String[] args) {
    JTextField myTextField = new JTextField();
    // Your code, set size and position of textfield
    panel.add(myTextField);
}

class ButtonHandler implements ActionListener {
    public void actionPerformed(ActionEvent event) {
        String text = myTextField.getText();
        myTextField.setText("");
        new BufferedWriter(new FileWriter("text.txt")).write(text).newLine().close();
        // the rest of your code
    }
}