Notepad evolved, refactored to Kotlin, on JDK11+

Notepad.kt

package javaproj

import java.awt.event.ActionEvent
import java.awt.event.ActionListener
import java.awt.event.WindowEvent
import java.io.*
import javax.swing.*
import kotlin.system.exitProcess
import javax.swing.JOptionPane.showMessageDialog as alert

/**
 * ! Java Swing | Create a simple text editor
 * https://www.geeksforgeeks.org/java-swing-create-a-simple-text-editor/
 * Refactored to Kotlin using Idea and own hands, removed some loops
 */
class Notepad internal constructor() : JFrame(), ActionListener {
    // Text component
    private var t: JTextPane // * https://stackoverflow.com/questions/11302982/jtextarea-consumes-a-lot-of-memory

    // Frame
    private var frame: JFrame = JFrame("editor v2")

    companion object {
        // Main class
        @JvmStatic
        fun main(args: Array<String>) {
            System.setProperty("awt.useSystemAAFontSettings", "off")
            System.setProperty("swing.aatext", "true")
            Notepad()
        }
    }

    // Constructor
    init {
        // Create a frame
        try {
            // I hate metal look and feel
            UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel")
        } catch (ignored: Exception) {
        }


        // Text component
        t = JTextPane()
        //scroll


        // Create a menubar
        val mb = JMenuBar()

        // Create amenu for menu
        val m1 = JMenu("File")

        // Create menu items
        val mi1 = JMenuItem("New")
        val mi2 = JMenuItem("Open")
        val mi3 = JMenuItem("Save")
        val mi9 = JMenuItem("Print")

        // Add action listener
        mi1.addActionListener(this)
        mi2.addActionListener(this)
        mi3.addActionListener(this)
        mi9.addActionListener(this)
        m1.add(mi1)
        m1.add(mi2)
        m1.add(mi3)
        m1.add(mi9)

        // Create amenu for menu
        val m2 = JMenu("Edit")

        // Create menu items
        val mi4 = JMenuItem("cut")
        val mi5 = JMenuItem("copy")
        val mi6 = JMenuItem("paste")

        // Add action listener
        mi4.addActionListener(this)
        mi5.addActionListener(this)
        mi6.addActionListener(this)

        m2.add(mi4)
        m2.add(mi5)
        m2.add(mi6)

        val mc = JMenuItem("close")

        mc.addActionListener(this)

        mb.add(m1)
        mb.add(m2)
        mb.add(mc)

        frame.jMenuBar = mb



        frame.add(JScrollPane(t)) // enabling scrolling
        frame.setSize(500, 500)
        frame.defaultCloseOperation = EXIT_ON_CLOSE
        frame.isVisible = true
    }

    //! If a button is pressed
    override fun actionPerformed(e: ActionEvent) {
        try {
            when (e.actionCommand) {
                "cut" -> t.cut()
                "copy" -> t.copy()
                "paste" -> t.paste()
                "Save" -> {
                    Thread {
                        // Create an object of JFileChooser class
                        val j = JFileChooser("f:")

                        // Invoke the showsSaveDialog function to show the save dialog
                        val r = j.showSaveDialog(null)
                        if (r == JFileChooser.APPROVE_OPTION) {

                            // Set the label to the path of the selected directory
                            val fi = File(j.selectedFile.absolutePath)
                            try {
                                // Create a file writer
                                val wr = FileWriter(fi, false)

                                // Create buffered writer to write
                                val w = BufferedWriter(wr)

                                // Write
                                w.write(t.text)
                                w.flush()
                                w.close()
                            } catch (evt: java.lang.Exception) {
                                alert(frame, evt.message)
                                evt.printStackTrace()
                            }
                        } else alert(frame, "the user cancelled the operation")
                    }.start()
                }
                "Print" -> {
                    // print the file
                    t.print()
                }
                "Open" -> {
                    // Create an object of JFileChooser class
                    val j = JFileChooser("f:")

                    // Invoke the showsOpenDialog function to show the save dialog
                    val r = j.showOpenDialog(null)

                    // If the user selects a file
                    if (r == JFileChooser.APPROVE_OPTION) {
                        // Set the label to the path of the selected directory
                        val fi = File(j.selectedFile.absolutePath)

                        // File reader
                        val fr = FileReader(fi)
                        val br = BufferedReader(fr)

                        //! Take the input from the file
                        val lines: String = br.readLines()
                            .joinToString("\n")

                        // Set the text
                        t.text = lines
                        System.gc()

                    } else alert(frame, "the user cancelled the operation")
                }
                "New" -> {
                    t.text = ""
                    System.gc()
                }
                "close" -> {
//                    frame.isVisible = false
//                    exitProcess(0)

                    frame.dispatchEvent(WindowEvent(frame,WindowEvent.WINDOW_CLOSING))
                }
            }  //end of when
        } catch (evt: java.lang.Exception) {
            alert(frame, evt.message)
            evt.printStackTrace()
        }
    }  //end of listener
}  //end of class