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Android app development is one of the essential skills in the modern era. In particular, Java is a widely used language for Android application development, providing excellent compatibility with the Android framework and various libraries for scalability. This course will explain in detail the process of developing and releasing Android apps using Java.

1. Setting Up the Environment

To develop an app, you must first set up the development environment. Android Studio is the official IDE (Integrated Development Environment) for Android development.

• Install Android Studio: Download and install Android Studio from Google’s official website.
• Install Java JDK: Install the Java Development Kit (JDK) to enable Java application development.
• Configure SDK: Set up the SDK (Software Development Kit) within Android Studio.

2. Creating a Project

This section covers the process of opening Android Studio and creating a new project.

1. Run Android Studio and click ‘Start a new Android Studio project’.
2. Select a project template. You may choose ‘Empty Activity’ as the default.
3. Set the project name, package name, save location, and language (Java), then click ‘Finish’.

3. Designing the User Interface

Now, let’s design the app’s user interface (UI) using XML.

        <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical">

            <TextView
                android:id="@+id/welcome_text"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Hello, welcome to Android app development!"/>

            <Button
                android:id="@+id/start_button"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Get Started"/>

        </LinearLayout>
        

4. Implementing Functionality

Now, we will implement features that interact with the UI through Java code. Let’s add a button click event.

        package com.example.myfirstapp;

        import androidx.appcompat.app.AppCompatActivity;
        import android.os.Bundle;
        import android.view.View;
        import android.widget.Button;
        import android.widget.TextView;

        public class MainActivity extends AppCompatActivity {
            @Override
            protected void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.activity_main);

                final TextView welcomeText = findViewById(R.id.welcome_text);
                Button startButton = findViewById(R.id.start_button);

                startButton.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        welcomeText.setText("Starting the app!");
                    }
                });
            }
        }
        

5. Debugging and Testing

Before launching the app, you need to ensure that all necessary features work properly. You can use the Android Emulator or perform tests on a real device for this purpose.

• Debugging: Check error messages and use Logcat to resolve issues.
• Testing: Check how the app functions on various screen sizes and resolutions.

6. Preparing for App Release

Once the app is complete, you need to prepare for its release.

1. App Signing: To distribute the app on Google Play, you need to sign it. This is an important process for secure app distribution.
2. Creating a Release Build: Create a release build separate from the debug build. Select ‘Build’ from the Android Studio menu, then choose ‘Build Bundle(s)/APK(s)’.

7. Distributing on Google Play Store

To distribute the app on Google Play, you must follow certain procedures:

1. Creating a Google Play Developer Account: Sign up for a Google Play Console and create a developer account.
2. Registering the App: Click ‘Add App’ and fill in various information to register the app.
3. Uploading the APK: Upload the created release build.
4. Adding Marketing Images: Add the app icon, screenshots, and description.
5. Launch: Once all processes are complete, launch the app.

8. Managing App Updates

After launching the app, it requires ongoing updates and management. It’s important to fix bugs and add new features by reflecting user feedback.

Conclusion

Developing Android apps using Java is an interesting and rewarding process. By following several steps, you can release and maintain an app that provides value to users. I hope this course enables you to develop and successfully launch the app you dream of.

Android app development is one of the popular fields for many developers today. In particular, Java is one of the most widely used programming languages for Android app development. In this course, we will explain in detail how to develop and run Android apps using Java. This course will comprehensively cover everything from setting up the Android development environment to creating and running a simple example app.

1. Setting Up the Android Development Environment

To start Android app development, you must first set up the development environment. Officially, install Android Studio, which is provided by Google. Android Studio is an integrated development environment (IDE) for developing Android apps that offers various features to help make development easier.

1.1 Installing Android Studio

1. Visit the Android Studio website (developer.android.com/studio) and download the installation file.
2. Run the downloaded file and follow the installation wizard to proceed with the installation.
3. Once installation is complete, run Android Studio.

1.2 Installing JDK

To develop Android apps, you need the Java Development Kit (JDK). If the JDK is not already installed, you must download and install it from Oracle’s official website.

2. Creating a New Project

Once the development environment is set up, let’s create a new Android project. Please follow the steps below.

1. Run Android Studio and click ‘New Project’.
2. Select ‘Empty Activity’ and click the ‘Next’ button.
3. Choose the project name, package name, project location, and language (Java), then click the ‘Finish’ button.

3. Understanding the App Structure

An Android app consists of multiple files and folders. The main components are as follows:

• AndroidManifest.xml: A file that defines the app’s metadata. It allows you to configure the app’s components, permissions, API levels, etc.
• res/: A folder that stores resource files (images, layouts, strings, etc.) used by the app.
• java/: A folder where Java source files are stored, which is where you implement the main logic of the app.

4. Developing a Simple App

Here, we will create a simple app that displays the message “Hello, Android!” when the button is clicked.

4.1 Setting Up the Layout

First, modify the activity_main.xml file to add a button and a text view. This file is located in the res/layout/ folder. Please enter the following code:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/text_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello!"
        android:layout_centerInParent="true"
        android:textSize="24sp" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Click Me"
        android:layout_below="@id/text_view"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="20dp" />

</RelativeLayout>

4.2 Writing the Java Code

Next, modify the main activity file (MainActivity.java) to handle the button click event. It is located in the java/com.example.yourapp/ folder. Please modify it with the following code:

package com.example.yourapp;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    private TextView textView;
    private Button button;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textView = findViewById(R.id.text_view);
        button = findViewById(R.id.button);

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                textView.setText("Hello, Android!");
            }
        });
    }
}

5. Running the App

Now it’s time to run the app. Please follow the steps below.

1. Click the “Run” button on the Android Studio toolbar.
2. Select a virtual device or physical device. If you want to use a virtual device, you need to set up an Android Virtual Device (AVD). If AVD is not installed by default, you can set it up through the AVD Manager.
3. Once the app is built, it will run on the selected device.

5.1 Setting Up AVD

To set up a virtual device, follow these steps:

1. Click the “AVD Manager” icon in Android Studio.
2. Click “Create Virtual Device” and choose the desired device.
3. Select the system image to use for the selected device.
4. Click “Finish” to create the virtual device.

6. App Execution Result

If the app runs successfully, clicking the button will display the message “Hello, Android!” in the TextView. This simple app helps you understand the basic flow of Android development.

7. Conclusion

In this course, we covered the start of Android app development using Java. We explained the installation of Android Studio, creating a new project, understanding app structure, developing and running a simple app in a total of 7 steps. Through this process, developers can easily create and run basic apps, and later move on to more complex app development.

Now you have the fundamentals to develop your own apps using Java and Android Studio. In the future, explore various features related to Java and Android development through more extensive exploration.

8. Next Steps: Getting Familiar

To take a step further, it is essential to use various resources to enhance your app. It would be beneficial to explore the following topics:

• Android UI Components: ListView, RecyclerView, Toolbar, etc.
• Data Storage: SQLite, Shared Preferences
• Networking: Retrofit, Volley
• Multimedia: Camera, audio recording functionality, etc.

All these processes will be important guides to help you grow into a better Android developer.

In the Android platform, Activity is a key component that constitutes the user interface.
An activity can be viewed as a screen where the user can perform specific tasks and represents the basic building block of an Android application.

What is an Activity?

An activity is a screen that displays a specific task to the user. For example, screens where users can click buttons or
input information are all considered activities. Each activity exists independently and allows users
to perform various tasks by switching between multiple activities.

Activity Lifecycle

An activity has states such as creation, start, pause, resume, stop, and destruction, and these states are managed through
the activity’s lifecycle. Understanding the activity lifecycle is crucial for app development.

Lifecycle Methods

• onCreate(): Called when the activity is first created. Initializes UI and performs setup tasks.
• onStart(): Called when the activity is about to become visible to the user.
• onResume(): Called when the activity starts interacting with the user.
• onPause(): Called when another activity is about to start interacting with the user. Used to save important tasks.
• onStop(): Called when the activity is no longer visible to the user.
• onDestroy(): Called when the activity is finishing. Used to clean up remaining resources to prevent memory leaks.

Activity Example

Below is a sample code that creates a basic activity and implements lifecycle methods.
In this example, the current state will be displayed in a TextView.

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView textView = findViewById(R.id.textView);
        textView.setText("onCreate called");
    }

    @Override
    protected void onStart() {
        super.onStart();
        TextView textView = findViewById(R.id.textView);
        textView.setText("onStart called");
    }

    @Override
    protected void onResume() {
        super.onResume();
        TextView textView = findViewById(R.id.textView);
        textView.setText("onResume called");
    }

    @Override
    protected void onPause() {
        super.onPause();
        TextView textView = findViewById(R.id.textView);
        textView.setText("onPause called");
    }

    @Override
    protected void onStop() {
        super.onStop();
        TextView textView = findViewById(R.id.textView);
        textView.setText("onStop called");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        TextView textView = findViewById(R.id.textView);
        textView.setText("onDestroy called");
    }
}
    

Communication Between Intents and Activities

In Android, transitions between activities occur through Intents.
An intent is an object used to pass information from one activity to another or to call system components.

Intent Usage Example

Let’s look at sample code that creates two activities, where clicking a button in the first activity
transitions to the second activity.

// MainActivity.java
public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button button = findViewById(R.id.button);
        button.setOnClickListener(v -> {
            Intent intent = new Intent(MainActivity.this, SecondActivity.class);
            startActivity(intent);
        });
    }
}

// SecondActivity.java
public class SecondActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        TextView textView = findViewById(R.id.textView);
        textView.setText("This is the second activity.");
    }
}
    

Passing Data

When using intents, you can also pass data along. Let’s examine how to pass data via intents through
the following example.

// MainActivity.java (Adding data transfer)
public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button button = findViewById(R.id.button);
        button.setOnClickListener(v -> {
            Intent intent = new Intent(MainActivity.this, SecondActivity.class);
            intent.putExtra("message", "Hello, Second Activity");
            startActivity(intent);
        });
    }
}

// SecondActivity.java (Receiving data)
public class SecondActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        TextView textView = findViewById(R.id.textView);
        String message = getIntent().getStringExtra("message");
        textView.setText(message);
    }
}
    

Conclusion

Today we learned about activities and their lifecycle in Android app development,
transitions between activities via intents, and how to pass data.
These concepts are fundamental to Android app development and will serve as a starting point
for creating more complex apps.
In future lessons, we will cover more features and UI elements, so please stay tuned.

One of the most important elements in the process of developing an Android app is the app’s configuration files. In this article, we will analyze the main configuration files used in Android app development and explore how they affect the app’s operation. Android apps are primarily composed of XML format configuration files and Java code, and we will focus on how these two types of files interact.

1. Configuration Files of Android Apps

Configuration files of Android apps can be broadly divided into two categories: manifest files and resource files. These files provide basic information about the app and define various resources such as the app’s UI, strings, images, and more.

1.1. Manifest File (AndroidManifest.xml)

The manifest file is a composite file for Android apps that must contain all the information necessary for the app to function properly. The AndroidManifest.xml file defines the metadata related to the app’s components (activities, services, broadcast receivers, etc.).

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.myapp">

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

        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

    </application>

</manifest>

The code above shows the basic structure of the manifest file. The key elements are as follows:

• package: Defines the unique package name of the app.
• application: Specifies the app’s fundamental properties, including icon, theme, label, and more.
• activity: Defines the activities that the app will use, specifying the main activity and adding an intent filter to start it.

1.2. Resource Files

Resource files define various resources related to the app’s UI and business logic. This includes strings, images, layouts, and styles. Resource files are located within the project’s /res directory and support various resolutions and languages through a folder structure.

1.2.1. String Resources (res/values/strings.xml)

<resources>
    <string name="app_name">My App</string>
    <string name="welcome_message">Welcome!</string>
</resources>

String resources define strings that can be reused in other UI components, which helps avoid hard-coded strings in layout files.

1.2.2. Layout Resources (res/layout/activity_main.xml)

Layout files define the UI of the app. In Android, layouts can be defined in XML format.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/welcome_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/welcome_message"/>

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button"/>

</LinearLayout>

The layout code above defines a LinearLayout arranged vertically. It contains a TextView and a Button, with the TextView using the welcome_message defined in the string resources.

2. Role of Configuration Files When Running the App

When an Android app is run, the information in the manifest file is interpreted by the system to meet the app’s requirements. The activities defined in the manifest serve as the starting point that determines what UI will be shown when the user launches the app. For instance, when the user clicks the app icon, MainActivity is executed based on the MAIN action and LAUNCHER category set in the manifest file.

Resource files seamlessly connect the information of UI components with the business logic. Layout files define how UI elements are arranged, and these elements can be easily referenced in the code.

3. Comprehensive Example

Now, through a practical example, we will show how the manifest file and resource files actually work. The complete app is structured to display a welcome message to the user and navigate to another page upon button click.

3.1. Manifest File (AndroidManifest.xml)

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.welcomeapp">

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

        <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=".SecondActivity"></activity>

    </application>

</manifest>

3.2. String Resources (res/values/strings.xml)

<resources>
    <string name="app_name">Welcome App</string>
    <string name="welcome_message">Welcome!</string>
    <string name="second_activity_title">Second Activity</string>
</resources>

3.3. Main Layout (res/layout/activity_main.xml)

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/welcome_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/welcome_message"/>

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Next Page"/>

</LinearLayout>

3.4. Second Layout (res/layout/activity_second.xml)

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/second_activity_title"/>

</LinearLayout>

3.5. MainActivity.java

package com.example.welcomeapp;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        TextView welcomeText = findViewById(R.id.welcome_text);
        Button nextButton = findViewById(R.id.button);

        nextButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, SecondActivity.class);
                startActivity(intent);
            }
        });
    }
}

3.6. SecondActivity.java

package com.example.welcomeapp;

import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;

public class SecondActivity extends AppCompatActivity {
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
    }
}

4. Conclusion

Configuration files play a central role in Android app development and are essential for understanding the app’s structure and functionality. The manifest file defines how the app is executed and how the components interact, while the resource files provide the necessary elements to adjust what is presented to the user. Understanding their relationships is key to successful app development.

Although analyzing the configuration files of an Android app can be challenging, I hope this article is helpful. It aims to enhance your understanding of how each component connects to complete the app, leading to more effective app development.

One of the most important concepts in Android app development is the Activity and its lifecycle. An Activity is a component that makes up the user interface (UI) and represents a screen that users interact with. In this course, we will explore the Activity lifecycle in Android app development using Java and explain the tasks that can be performed at each stage.

What is an Activity?

An Activity is a component that represents the user interface of an Android application and corresponds to a single screen within the app. Everything that the user interacts with in the app happens within an Activity. Activities include various UI elements to display information to the user and handle user interactions.

Activity Lifecycle

The Activity lifecycle refers to the flow of states and transitions from the creation to the destruction of an Activity. The Android system manages the Activity lifecycle, with the following key methods:

• onCreate()
• onStart()
• onResume()
• onPause()
• onStop()
• onDestroy()
• onRestart()

1. onCreate()

The onCreate() method is called when the Activity is first created. It primarily performs UI setup and basic initialization tasks. In this method, the layout is set and initial variables are defined.

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
}

2. onStart()

The onStart() method is called just before the Activity becomes visible to the user. In this method, the UI can be initialized, signaling that the Activity is ready for user interaction.

@Override
protected void onStart() {
    super.onStart();
    // Handle just before the Activity is shown to the user
}

3. onResume()

The onResume() method is called when the Activity is about to become the foreground activity. Common tasks performed here include updating the UI or starting animations.

@Override
protected void onResume() {
    super.onResume();
    // Update UI or start animations
}

4. onPause()

The onPause() method is called when another Activity is starting or this Activity is being paused. In this method, data should be saved, or animations should be stopped. It indicates that the user is no longer actively using this Activity.

@Override
protected void onPause() {
    super.onPause();
    // Save data and stop animations
}

5. onStop()

The onStop() method is called when the Activity is no longer visible to the user. At this stage, resources should be released, and tasks that need to be handled when the Activity is not visible should be performed.

@Override
protected void onStop() {
    super.onStop();
    // Release resources and perform cleanup
}

6. onDestroy()

The onDestroy() method is called when the Activity is finishing. In this method, memory can be released and final cleanup tasks can be carried out. However, this method may not be called, so it is advisable to save important data in onPause() or onStop().

@Override
protected void onDestroy() {
    super.onDestroy();
    // Final cleanup tasks
}

7. onRestart()

The onRestart() method is called when the Activity is being restarted after stopping. This method is called after onStop(). Here, tasks to restore the previous state are performed.

@Override
protected void onRestart() {
    super.onRestart();
    // Tasks when restarting the Activity
}

Lifecycle Example

Now, let’s create an example that incorporates the Activity lifecycle explained earlier. In this example, we will log the Activity’s state through button clicks.

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button button = findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.d(TAG, "Button clicked!");
            }
        });
    }

    @Override
    protected void onStart() {
        super.onStart();
        Log.d(TAG, "onStart called");
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.d(TAG, "onResume called");
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.d(TAG, "onPause called");
    }

    @Override
    protected void onStop() {
        super.onStop();
        Log.d(TAG, "onStop called");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.d(TAG, "onDestroy called");
    }
}

Managing the Lifecycle

Managing the Activity lifecycle has a significant impact on the performance of the app and the user experience. Data that is necessary during the creation and destruction process should be saved in onPause() or onStop(), and the UI should be updated in onResume() when changes occur.

Saving State

When an Activity is restarted after being stopped, it may be necessary to save its state. You can use the onSaveInstanceState() method for this purpose. Below is an example of how to save state.

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putString("key", "value");
}

Saved state can be restored in onCreate() or onRestoreInstanceState().

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    
    if (savedInstanceState != null) {
        String value = savedInstanceState.getString("key");
    }
}

Conclusion

The Android Activity lifecycle is one of the fundamental components of an app, and understanding it and managing it effectively is important. Performing tasks correctly according to each stage of the lifecycle can provide a better user experience. I hope this course provides you with a basic understanding of the Activity lifecycle.

In conclusion, I have explained the Activity lifecycle in Android app development using Java. Deepen your understanding through practical exercises, and make good use of the lifecycle in various situations!