------------------------------------------------------------------------------------
      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">

    <FrameLayout
        android:id="@+id/frameLayout"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginStart="10dp"
        android:layout_marginEnd="10dp"
        app:layout_constraintBottom_toTopOf="@+id/fragment1_btn"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_goneMarginTop="10dp">

    </FrameLayout>

    <Button
        android:id="@+id/fragment1_btn"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:text="Go Frag1"
        android:textAllCaps="false"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/fragment2_btn"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/frameLayout" />

    <Button
        android:id="@+id/fragment2_btn"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:text="Go Frag2"
        android:textAllCaps="false"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toEndOf="@+id/fragment1_btn"
        app:layout_constraintTop_toBottomOf="@+id/frameLayout" />

</androidx.constraintlayout.widget.ConstraintLayout>



*** <  res/layout 에 fragment_1.xml 과 fragment_2.xml 를  추가한다.  > ************
------------------------------------------------------------------------------------
      fragment_1.xml
-------------------------------------------------------------------------------------
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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=".Fragment1">

    <!-- TODO: Update blank fragment layout -->
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="126dp"
        android:background="@color/white"
        android:text="여기는\nFragment 1 입니다."
        android:textAllCaps="false"
        android:textSize="40sp"
        android:textColor="#3949AB"
        android:layout_marginTop="100dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</FrameLayout>

------------------------------------------------------------------------------------
      fragment_2.xml
-------------------------------------------------------------------------------------
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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=".Fragment2">

    <!-- TODO: Update blank fragment layout -->
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="여기는\nfragment 2 입니다."
        android:textAllCaps="false"
        android:textSize="40sp"
        android:textColor="#4AAB39"
        android:background="#F4DE7A"
        android:layout_marginTop="100dp"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintBottom_toBottomOf="parent" />
    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/sun"
        />

</FrameLayout>

------------------------------------------------------------------------------------
    MainActivity.kt
-------------------------------------------------------------------------------------
class MainActivity : AppCompatActivity() {
    private val binding by lazy { ActivityMainBinding.inflate(layoutInflater) }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        //setContentView(R.layout.activity_main)
        setContentView(binding.root)

        binding.run {  // 1번
            fragment1Btn.setOnClickListener{
                setFragment(Fragment1()) //3번
            }
            fragment2Btn.setOnClickListener {
                setFragment(Fragment2())
            }
        }
    }

    private fun setFragment(frag : Fragment) {  //2번
        supportFragmentManager.commit {
            replace(R.id.frameLayout, frag)
            setReorderingAllowed(true)
            addToBackStack("")
        }
    }
}

*** <  app/java 에 Fragment1.kt 과 Fragment2.kt 를  추가한다.  > ************
------------------------------------------------------------------------------------
    Fragment1.kt
-------------------------------------------------------------------------------------
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private const val ARG_PARAM1 = "param1"
private const val ARG_PARAM2 = "param2"

/**
 * A simple [Fragment] subclass.
 * Use the [Fragment1.newInstance] factory method to
 * create an instance of this fragment.
 */
class Fragment1 : Fragment() {
    // TODO: Rename and change types of parameters
    private var param1: String? = null
    private var param2: String? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {
            param1 = it.getString(ARG_PARAM1)
            param2 = it.getString(ARG_PARAM2)
        }
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_1, container, false)
    }

    companion object {
        /**
        * Use this factory method to create a new instance of
        * this fragment using the provided parameters.
        *
        * @param param1 Parameter 1.
        * @param param2 Parameter 2.
        * @return A new instance of fragment Fragment1.
        */
        // TODO: Rename and change types and number of parameters
        @JvmStatic
        fun newInstance(param1: String, param2: String) =
            Fragment1().apply {
                arguments = Bundle().apply {
                    putString(ARG_PARAM1, param1)
                    putString(ARG_PARAM2, param2)
                }
            }
    }
}

------------------------------------------------------------------------------------
    Fragment2.kt
-------------------------------------------------------------------------------------
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private const val ARG_PARAM1 = "param1"
private const val ARG_PARAM2 = "param2"

/**
 * A simple [Fragment] subclass.
 * Use the [Fragment2.newInstance] factory method to
 * create an instance of this fragment.
 */
class Fragment2 : Fragment() {
    // TODO: Rename and change types of parameters
    private var param1: String? = null
    private var param2: String? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {
            param1 = it.getString(ARG_PARAM1)
            param2 = it.getString(ARG_PARAM2)
        }
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_2, container, false)
    }

    companion object {
        /**
        * Use this factory method to create a new instance of
        * this fragment using the provided parameters.
        *
        * @param param1 Parameter 1.
        * @param param2 Parameter 2.
        * @return A new instance of fragment Fragment2.
        */
        // TODO: Rename and change types and number of parameters
        @JvmStatic
        fun newInstance(param1: String, param2: String) =
            Fragment2().apply {
                arguments = Bundle().apply {
                    putString(ARG_PARAM1, param1)
                    putString(ARG_PARAM2, param2)
                }
            }
    }
}


------------------------------------------------------------------------------------------------
    build.gradle(Module)
-----------------------------------------------------------------------------------------------
// 안드로이드 스튜디오 4.0 이상
android {
    ...
    buildFeatures {
        viewBinding = true
    }
}