Utility Class

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <EditText
        android:id="@+id/etInput"
        android:layout_width="0dp"
        android:layout_height="50sp"
        android:layout_marginStart="24dp"
        android:layout_marginTop="32dp"
        android:layout_marginEnd="24dp"
        android:ems="10"
        android:hint="Enter Text"
        android:inputType="text"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:autofillHints="" />

    <ImageView
        android:id="@+id/ivResult"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toTopOf="@+id/tvResult"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/etInput"
        app:srcCompat="@drawable/check" />

    <com.google.android.material.floatingactionbutton.FloatingActionButton


        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginEnd="24dp"
        android:layout_marginBottom="24dp"
        android:clickable="true"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:srcCompat="@android:drawable/ic_menu_info_details" />

    <TextView
        android:id="@+id/tvResult"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="32dp"
        android:text="Is a Palindrome"
        android:textSize="34sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/fab"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.kt

package edu.piedmont.cs.palindromepractice2

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.text.Editable
import android.text.TextWatcher
import android.util.Log
import android.view.View
import android.widget.EditText
import android.widget.ImageView
import android.widget.TextView
import com.google.android.material.floatingactionbutton.FloatingActionButton
import com.google.android.material.snackbar.Snackbar
import edu.piedmont.cs.palpracjava.Palindrome

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val tv = findViewById<TextView>(R.id.tvResult)
        val iv = findViewById<ImageView>(R.id.ivResult)
        val fab = findViewById<FloatingActionButton>(R.id.fab)
        val input = findViewById<EditText>(R.id.etInput)
        val textWatcher: TextWatcher = object : TextWatcher {
            override fun beforeTextChanged(charSequence: CharSequence, i: Int, i1: Int, i2: Int) {}
            override fun onTextChanged(charSequence: CharSequence, i: Int, i1: Int, i2: Int) {}
            override fun afterTextChanged(editable: Editable) {
                val entered = input.text.toString()
                if (Palindrome.check(entered)) {
                    tv.text = "is a palindrome"
                    Log.v(TAG, "is a palindrome")
                    iv.setImageResource(R.drawable.check)
                } else {
                    Log.v(TAG, "is not a palindrome")
                    tv.text = "is not a palindrome"
                    iv.setImageResource(R.drawable.x)
                }
            }
        }
        input.addTextChangedListener(textWatcher)

        fab.setOnClickListener { view ->
            Snackbar.make(view, "Go Piedmont Lions!", Snackbar.LENGTH_LONG)
                .setAction("Action", null).show()
        }
    }

    companion object {
        private const val TAG = "Pal"
    }
}

Palindrome.kt

package edu.piedmont.cs.palpracjava

object Palindrome {
    fun check(_s: String): Boolean {
        return check(_s, 0, _s.length - 1)
    }

    private fun check(_s: String, _start: Int, _end: Int): Boolean {

        // base case
        var end = _end
        var start = _start;
        if (_start >= _end) return true

        // do some work
        while (!Character.isLetterOrDigit(_s[start])) start++
        while (!Character.isLetterOrDigit(_s[end])) end--
        val downcaseStart = _s[_start].lowercaseChar()
        val downcaseEnd = _s[_end].lowercaseChar()
        // called simplified version
        return if (downcaseStart != downcaseEnd) false else check(_s, _start + 1, _end - 1)
    }
}