File Editor

FileEditor.java

package kis.sample;

import java.awt.BorderLayout;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.List;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;

public class FileEditor {
    public static void main(String[] args) {
        var f = new JFrame("editor");
        var textarea = new JTextArea();
        f.add(textarea);
        
        var p = new JPanel();
        f.add(BorderLayout.NORTH, p);
        
        var loadButton = new JButton("Load");
        loadButton.addActionListener(ae -> {
            var dialog = new JFileChooser();
            if (dialog.showOpenDialog(f) != JFileChooser.APPROVE_OPTION) {
                return;
            }
            String separator = System.getProperty("line.separator");
            Path selected = dialog.getSelectedFile().toPath();
            try {
                List<String> lines = Files.readAllLines(selected);
                textarea.setText("");
                lines.forEach(line -> textarea.append(line + "\n"));
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        });
        p.add(loadButton);
        
        var saveButton = new JButton("Save");
        saveButton.addActionListener(ae -> {
            var dialog = new JFileChooser();
            if (dialog.showSaveDialog(f) != JFileChooser.APPROVE_OPTION) {
                return;
            }
            String separator = System.getProperty("line.separator");
            Path selected = dialog.getSelectedFile().toPath();
            try {
                Files.write(selected, List.of(
                        textarea.getText().replace("\n", separator)));
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        });
        p.add(saveButton);
        
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setSize(400, 300);
        f.setVisible(true);
    }
}