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

This is the way I would write to a file. I will let you convert this code into your GUI for practice. See more on BufferedWriter and FileWriter

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.util.Scanner;

public class Files {

    public static void main(String args[]){

        System.out.print("Enter Text: ");
        Scanner scan = new Scanner(System.in);
        String text = scan.nextLine();
        FileWriter fWriter = null;
        BufferedWriter writer = null;
        try {
          fWriter = new FileWriter("text.txt");
          writer = new BufferedWriter(fWriter);
          writer.write(text);
          writer.newLine();
          writer.close();
          System.err.println("Your input of " + text.length() + " characters was saved.");
        } catch (Exception e) {
            System.out.println("Error!");
        }
    }

}

Answer 2

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
    }
}