public abstract class Activity {

    // Called when the activity is first created.
    protected void onCreate(Bundle savedInstanceState) {}

    // Called when the activity is being restarted after being stopped.
    protected void onRestart() {}

    // Called before the activity is destroyed.
    protected void onDestroy() {}
    
    // Called when the activity becomes visible to the user.
    protected void onStart() {}

    // Called when the activity starts interacting with the user.
    protected void onResume() {}

    // Called when the system is about to pause the activity (e.g., another activity comes into focus).
    protected void onPause() {}

    // Called when the activity is no longer visible to the user.
    protected void onStop() {}

    // Optional: Called to save instance state before activity is paused or stopped.
    protected void onSaveInstanceState(Bundle outState) {}

    // Optional: Called to restore state when the activity is recreated.
    protected void onRestoreInstanceState(Bundle savedInstanceState) {}
}

chase@laptop:/tmp$ unzip MyApp.apk 
Archive:  MyApp.apk
  inflating: AndroidManifest.xml     
  inflating: META-INF/MANIFEST.MF    
 extracting: assets/filter/amaro_mask1.jpg  
 extracting: assets/filter/amaro_mask2.jpg  
...
chase@laptop:/tmp$ ls
AndroidManifest.xml  assets  build-data.properties  classes.dex  META-INF  res  resources.arsc

chase@laptop:/tmp$ cat AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:versionCode="1"
    android:versionName="1.0">

    <!-- Beware that these values are overridden by the build.gradle file -->
    <uses-sdk android:minSdkVersion="15" android:targetSdkVersion="26" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">

        <!-- This name is resolved to com.example.myapp.MainActivity
             based on the namespace property in the build.gradle file -->
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <activity
            android:name=".DisplayMessageActivity"
            android:parentActivityName=".MainActivity" />
    </application>
</manifest>

# This directory holds uncompiled resources used by the application, like images, 
# XML layouts, and strings. These are referenced in code using resource IDs.
chase@chase-laptop:/tmp/apk/res$ /bin/tree
.
├── anim
│   ├── abc_fade_in.xml
│   ├── abc_fade_out.xml
│   ├── abc_grow_fade_in_from_bottom.xml
│   ├── abc_popup_enter.xml
├── color
│   ├── abc_btn_colored_borderless_text_material.xml
│   ├── abc_hint_foreground_material_dark.xml
│   ├── abc_hint_foreground_material_light.xml
│   ├── abc_primary_text_disable_only_material_dark.xml
│   ├── abc_primary_text_disable_only_material_light.xml
├── color-v11
│   ├── abc_background_cache_hint_selector_material_dark.xml
│   └── abc_background_cache_hint_selector_material_light.xml
├── color-v23
│   ├── abc_btn_colored_borderless_text_material.xml
│   ├── abc_color_highlight_material.xml
│   ├── abc_tint_btn_checkable.xml
│   ├── abc_tint_default.xml
│   ├── abc_tint_edittext.xml
├── drawable
│   ├── abc_btn_borderless_material.xml
│   ├── abc_btn_check_material.xml
│   ├── abc_btn_colored_material.xml
│   ├── abc_btn_default_mtrl_shape.xml
│   ├── abc_btn_radio_material.xml
│   ├── abc_cab_background_internal_bg.xml
│   ├── abc_cab_background_top_material.xml
│   ├── abc_dialog_material_background.xml
│   ├── abc_edit_text_material.xml
├── drawable-hdpi-v4
│   ├── abc_ab_share_pack_mtrl_alpha.9.png
│   ├── abc_btn_check_to_on_mtrl_000.png
│   ├── abc_btn_check_to_on_mtrl_015.png
│   ├── abc_btn_radio_to_on_mtrl_000.png
│   ├── abc_btn_radio_to_on_mtrl_015.png
│   ├── abc_btn_switch_to_on_mtrl_00001.9.png
│   ├── abc_btn_switch_to_on_mtrl_00012.9.png
│   ├── abc_cab_background_top_mtrl_alpha.9.png
│   ├── abc_ic_commit_search_api_mtrl_alpha.png
│   ├── abc_ic_menu_copy_mtrl_am_alpha.png
│   ├── abc_ic_menu_cut_mtrl_alpha.png
│   ├── abc_ic_menu_paste_mtrl_am_alpha.png
│   ├── abc_ic_menu_selectall_mtrl_alpha.png
│   ├── abc_ic_menu_share_mtrl_alpha.png
│   ├── abc_ic_star_black_16dp.png
│   ├── abc_ic_star_black_36dp.png
│   ├── abc_ic_star_black_48dp.png
│   ├── abc_ic_star_half_black_16dp.png
│   ├── abc_ic_star_half_black_36dp.png
│   ├── abc_ic_star_half_black_48dp.png

// File: Fibonacci.kt
fun fib(n: Int): Int {
    if (n <= 1)
    	n
    else
    	fib(n - 1) + fib(n - 2)
}

fun main() {
    val number = 10
    println("Fibonacci of \$number is: \${fib(number)}")
}

public final class FibonacciKt {
  public static final int fib(int);
    Code:
       0: iload_0
       1: iconst_1
       2: if_icmpgt     7
       5: iload_0
       6: ireturn
       7: iload_0
       8: iconst_1
       9: isub
      10: invokestatic  #13                 // Method fib:(I)I
      13: iload_0
      14: iconst_2
      15: isub
      16: invokestatic  #13                 // Method fib:(I)I
      19: iadd
      20: ireturn

  public static final void main();
    Code:
       0: bipush        10
       2: istore_0
       3: getstatic     #19                 // Field java/lang/System.out:Ljava/io/PrintStream;
       6: new           #25                 // class java/lang/StringBuilder
       9: dup
      10: invokespecial #27                 // Method java/lang/StringBuilder."<init>":()V
      13: ldc           #29                 // String Fibonacci of 
      15: invokevirtual #33                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      18: iload_0
      19: invokevirtual #36                 // Method java/lang/StringBuilder.append:(I)Ljava/lang/StringBuilder;
      22: ldc           #38                 // String  is: 
      24: invokevirtual #33                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      27: iload_0
      28: invokestatic  #40                 // Method fib:(I)I
      31: invokevirtual #36                 // Method java/lang/StringBuilder.append:(I)Ljava/lang/StringBuilder;
      34: invokevirtual #44                 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
      37: invokevirtual #48                 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
      40: return
}

// File: NativeLib.kt
class NativeLib {
    companion object {
        init {
            System.loadLibrary("native") // Load the shared library named "native"
        }

        @JvmStatic external fun fib(n: Int): Int // Declare external native method
    }
}