SeeKeyEvents.scala

import javax.swing._
 
val f = new JFrame
val p = f.getContentPane.asInstanceOf[JComponent]
p.addKeyListener {
  new java.awt.event.KeyAdapter {
    override def keyPressed (e: java.awt.event.KeyEvent): Unit = println(e)
    override def keyReleased(e: java.awt.event.KeyEvent): Unit = println(e)
    override def keyTyped   (e: java.awt.event.KeyEvent): Unit = println(e)
  }
}
f.setSize(200, 200)
f.setVisible(true)
p.requestFocus()

import javax.swing._
import java.awt.event.{InputEvent, KeyEvent}
val f = new JFrame
val p = new JPanel(new java.awt.GridLayout(3,1))
f.setContentPane(p)
val ls = Array.fill(3)(new JLabel("-"))
ls.foreach(p.add)
p.addKeyListener {
  new java.awt.event.KeyAdapter {
    def apply(i: Int, e: KeyEvent): Unit = 
      ls(i).setText(InputEvent.getModifiersExText(e.getModifiersEx))
    override def keyPressed (e: KeyEvent): Unit = apply(0, e)
    override def keyReleased(e: KeyEvent): Unit = apply(1, e)
    override def keyTyped   (e: KeyEvent): Unit = apply(2, e)
  }
}
f.setSize(200, 200)
f.setVisible(true)
p.requestFocus()