Category: Java Android app development

Hello! In this course, we will cover various topics in Android app development using Java. In particular, we will take a deep dive into Java’s lambda functions and higher-order functions. Lambda functions, introduced in Java 8, serve to enhance the conciseness and readability of code. Additionally, higher-order functions are functions that can take other functions as parameters or return functions, and they are a very important concept in functional programming.

1. Basics of Java

Java is an object-oriented programming language with excellent portability, allowing it to run on various platforms. Since Android app development is based on Java, understanding the basics of Java is essential.

It is advisable to learn the fundamental syntax of Java, as well as key object-oriented programming concepts such as classes and objects, inheritance, and polymorphism before transitioning to Android development.

2. Java’s Lambda Functions

Lambda functions, also known as anonymous functions, allow you to write the body of the function inline. They enhance the readability of code and reduce the amount of code, making them particularly useful when writing callbacks or event listeners.

2.1. Syntax of Lambda Functions

        (argument1, argument2) -> { code to execute }
        

Let’s understand through a simple example. The code below defines and uses a lambda function that adds two numbers.

// Lambda function to add two numbers
BiFunction sum = (a, b) -> a + b;

// Usage example
int result = sum.apply(5, 10);
System.out.println(result);  // Output: 15
        

3. Java’s Higher-Order Functions

Higher-order functions are functions that take other functions as parameters or return them as results. In Java, higher-order functions are implemented using interfaces. They allow for code reusability and modularization.

3.1. Example of Higher-Order Functions

Below is a code example illustrating a higher-order function. This code takes two integers and performs different actions based on a specific condition.

import java.util.function.BiConsumer;

public class HigherOrderFunctionExample {
    public static void main(String[] args) {
        // Compare two numbers using a higher-order function and print the result
        compareAndAct(5, 10, (a, b) -> {
            if (a > b) {
                System.out.println("a is greater than b.");
            } else {
                System.out.println("a is less than or equal to b.");
            }
        });
    }

    static void compareAndAct(int a, int b, BiConsumer action) {
        action.accept(a, b);
    }
}
        

4. Lambda and Higher-Order Functions in Android

In Android, commonly used callback interfaces can be utilized with lambda expressions. For instance, when handling a Button click event, you can use a lambda as shown below.

Button myButton = findViewById(R.id.my_button);
myButton.setOnClickListener(v -> {
    // Action on button click
    Toast.makeText(this, "Button clicked.", Toast.LENGTH_SHORT).show();
});
        

5. Advantages of Lambda Functions and Higher-Order Functions

• Improved Readability: Function bodies can be expressed succinctly, making the code easier to understand.
• Code Reusability: Higher-order functions allow for code reuse and modularization of common behaviors.
• Version Control: Using lambdas and higher-order functions allows for easy separation of specific behaviors into functions, facilitating version control.

6. Conclusion

In this course, we have covered Java’s lambda functions and higher-order functions. These features are extremely useful in Android app development, enhancing code readability and ease of maintenance. In future app development, actively utilize these concepts to create better results.

By now, I believe you have a deeper understanding of Java, lambda functions, and higher-order functions. This will enable you to approach Android app development more profoundly. In the next course, we will proceed with hands-on practice building an actual Android app. Thank you.

Hello! In this course, we will cover Android app development using Java. Java has long been established as the fundamental language for Android development, and due to its stability and efficiency, it is a popular choice among many developers. In particular, ‘null safety’ is one of the very important topics in Java, as it can have a significant impact on the app’s stability and performance.

1. What is Null Safety?

Null safety refers to techniques that prevent errors that may arise from null values in programming languages. In Java, a null value represents a special value indicating ‘no value’. When accessing an object via a null reference, attempting an invalid reference may result in a NullPointerException. This can cause abnormal app termination and is a critical error that greatly affects user experience.

1.1 Causes of NullPointerException

NullPointerException can occur in the following situations:

• When calling a method on a null object
• When accessing a field of a null object
• When accessing a null array

Therefore, it is essential to check for null when using an object.

2. Null Safety in Java

Java does not guarantee null safety by default. However, developers can prevent these issues by coding null checks.

2.1 The Importance of Null Checks

By ensuring an object is not null before access, programmers can write safer code. For example, a null check can be performed like this:

if (object != null) {
        object.doSomething();
    } else {
        // Exception handling or alternative logic
    }

2.2 Using the Optional Class

The Optional class, introduced in Java 8, is a useful tool for implementing null safety. The Optional class is a container that indicates the existence of an object and can be used instead of null values.

Example Code:

import java.util.Optional;

    public class OptionalExample {
        public static void main(String[] args) {
            Optional optionalString = Optional.ofNullable(getString());

            optionalString.ifPresent(s -> System.out.println("Length of the string: " + s.length()));
        }

        public static String getString() {
            // Returns null
            return null;
        }
    }

In this example, the getString() method can return a null value. However, by using Optional, we can safely handle null values.

3. Null Safety in Android

Null safety is also an important factor in Android app development. Since null values can occur from user input or external data, they must be handled appropriately.

3.1 Comparison of Java and Kotlin

Kotlin is a language with built-in null safety and is often used alongside Java to maintain compatibility with Java. Kotlin distinguishes between nullable and non-nullable types, enabling safer code creation. In Kotlin, you can indicate nullability by using a ? when declaring variables.

Example Code (Kotlin):

fun main() {
        val name: String? = null
        println(name?.length ?: "It's null.")
    }

4. Developing Apps with Java and Null Safety in Android

When developing Android apps, it is important to consider null safety when interacting with user interface (UI) elements and various data sources. Here’s an example considering null safety.

4.1 Handling Button Click Events with Null Checks

Button myButton = findViewById(R.id.my_button);
    
    if (myButton != null) {
        myButton.setOnClickListener(view -> {
            // Actions on button click
        });
    }

4.2 Handling User Input

The following illustrates how to handle null values when receiving input from users:

EditText inputText = findViewById(R.id.input_text);
    String inputValue = inputText.getText().toString();
    
    if (!inputValue.isEmpty()) {
        // Process valid input value
    }

5. Conclusion

Null safety in Java is a crucial factor that affects the stability of apps and user experience. By utilizing null checks, the Optional class, and newer languages like Kotlin, developers can reduce the issues caused by null and create safer apps. Please remember these principles in your future app development!

In Android development, Intent is an essential element that enables interaction between applications. Understanding and utilizing intents is crucial for developing Android apps. In this article, we will take a detailed look at the concept of intents, their types, how to use them, example code, and more.

1. What is an Intent?

An intent is a message that requests the Android system to perform an action among components. Intents are used to start other Activities, Services, or Broadcast Receivers. They allow for data transfer and interaction within the app.

1.1. Components of an Intent

Intent intent = new Intent(context, TargetActivity.class);

• Context: The environment information of the layer where the intent is initiated.
• TargetActivity: The class of the Activity that will be started when the intent completes.

Intents can include optional information. You can add information using methods like:

intent.putExtra("key", "value");

2. Types of Intents

Intents in Android can be broadly classified into two types.

2.1. Explicit Intent

An explicit intent is used to start a specific component directly. It is primarily used to start another Activity within the same app.

Intent intent = new Intent(this, SecondActivity.class);
startActivity(intent);

2.2. Implicit Intent

An implicit intent relies on the action and data to find and execute an appropriate component. For example, a request to open a web page can be initiated as follows:

Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("http://www.example.com"));
startActivity(intent);

3. Passing Data with Intents

Data can be passed between two Activities using intents. This process consists of the following steps.

3.1. Passing Data

Data can be passed using intents in the following way:

Intent intent = new Intent(this, SecondActivity.class);
intent.putExtra("message", "Hello, SecondActivity!");
startActivity(intent);

3.2. Receiving Data

To receive the passed data, the receiving Activity can use the following code:

Intent intent = getIntent();
String message = intent.getStringExtra("message");
Toast.makeText(this, message, Toast.LENGTH_SHORT).show();

4. Flags of Intents

When using intents, flags can be set to modify the behavior of the intent. Commonly used flags include the following.

4.1. FLAG_ACTIVITY_NEW_TASK

This flag allows you to start an Activity in a new task.

Intent intent = new Intent(this, NewTaskActivity.class);
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(intent);

4.2. FLAG_ACTIVITY_CLEAR_TOP

Using this flag will clear all Activities above the existing Activity if it already exists and will start that Activity.

Intent intent = new Intent(this, TargetActivity.class);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);

5. Starting Services with Intents

Intents can also be used to start services. A service is a component that helps perform tasks in the background.

5.1. Defining and Starting a Service

Here’s how to define and start a service.

Intent intent = new Intent(this, MyService.class);
startService(intent);

5.2. Lifecycle of a Service

A service has the following lifecycle.

• onCreate(): Called when the service is created.
• onStartCommand(): Called when the service is started.
• onDestroy(): Called when the service is destroyed.

6. Broadcast Receiver and Intents

A Broadcast Receiver is a component that receives events occurring from the system or applications.

6.1. Sending a Broadcast

To send a broadcast using an intent, you can do the following:

Intent intent = new Intent("com.example.CUSTOM_EVENT");
sendBroadcast(intent);

6.2. Receiving a Broadcast

A Broadcast Receiver can be defined as follows:

public class MyReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "Broadcast received!", Toast.LENGTH_SHORT).show();
    }
}

7. Creating a Sample App using Intents

Now, let’s create a simple sample app using what you’ve learned about intents.

7.1. Package Structure

Our app will have the following package structure.

• com.example.intentapp
• com.example.intentapp.activities
• com.example.intentapp.receivers

7.2. MainActivity.java

The main Activity of the Android app uses the user interface (UI) and intents to call SecondActivity.

package com.example.intentapp.activities;

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

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(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, SecondActivity.class);
                intent.putExtra("message", "Hello, SecondActivity!");
                startActivity(intent);
            }
        });
    }
}

7.3. SecondActivity.java

SecondActivity receives and displays the data sent from MainActivity.

package com.example.intentapp.activities;

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

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

        Intent intent = getIntent();
        String message = intent.getStringExtra("message");

        TextView textView = findViewById(R.id.textView);
        textView.setText(message);
    }
}

7.4. Configuring AndroidManifest.xml

Register the new Activity in AndroidManifest.xml.

<activity android:name=".activities.SecondActivity"></activity>

8. Best Practices for Intents

Following some best practices while using intents can help create a more efficient app.

• Use explicit intents whenever possible. Implicit intents can impact performance.
• When passing data with intents, use appropriate data types. Parcelable objects are recommended over strings.
• Minimize the size of the data passed through intents.

9. Conclusion

Intents are a key concept in Android apps, enabling interaction and data transfer between applications. In this article, we explored the fundamental concepts of intents, their types, methods of data transfer, and their relationship with services and broadcast receivers. Based on this foundational knowledge, you can develop various Android apps.

Utilize intents in your future Android app development to add more features and create apps that provide an enhanced user experience. I hope you continue to improve your skills through various practices using intents!

In Android application development, the authentication feature is very important for protecting user information and data security. In this course, we will cover how to implement the authentication feature. We will explain step by step from basic concepts to actual code.

1. Understanding Authentication Feature

The authentication feature is the process of verifying who the user is. It is generally implemented through a username and password. However, nowadays various methods such as social login, biometrics, and two-factor authentication are being used. In Java Android apps, it can be implemented more easily through external libraries such as Firebase Authentication.

2. Setting Up the Project

Open Android Studio and create a new project. Follow the steps below:

1. Open Android Studio and click “New Project”.
2. Select Empty Activity and click Next.
3. Enter the project name and package name. For example: com.example.authenticationdemo.
4. Select Java as the language and click Finish.

3. Setting Up Firebase

Firebase is Google’s cloud service that makes it easy to implement authentication features. To set up a Firebase project, follow these steps:

1. Log in to the Firebase console (https://console.firebase.google.com/).
2. Add a new project.
3. In the project settings, click the Android icon to register the Android app.
4. Enter the package name and click “Add App”.
5. Download the google-services.json file and add it to the app folder.
6. Add the Google services plugin to your project’s build.gradle file.

buildscript {
    dependencies {
        classpath 'com.google.gms:google-services:4.3.10' // Make sure to update to the latest version
    }
}

allprojects {
    repositories {
        google()
        mavenCentral()
    }
}
        

7. Add the Firebase Authentication library to the app’s build.gradle file.

apply plugin: 'com.android.application'
apply plugin: 'com.google.gms.google-services'

dependencies {
    implementation 'com.google.firebase:firebase-auth:21.0.6' // Make sure to update to the latest version
}
        

4. Designing the Layout

To implement the authentication feature, you need to design the user interface (UI). Modify the res/layout/activity_main.xml file to create a UI like the following:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="16dp">

    <EditText
        android:id="@+id/editTextEmail"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Enter Email"/>

    <EditText
        android:id="@+id/editTextPassword"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Enter Password"
        android:inputType="textPassword"/>

    <Button
        android:id="@+id/buttonSignIn"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Log In"/>

    <Button
        android:id="@+id/buttonSignUp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Sign Up"/>
    
</LinearLayout>
    

5. Implementing the Authentication Logic

Now, let’s implement the actual authentication logic. Open the MainActivity.java file and add the following code.

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;

public class MainActivity extends AppCompatActivity {

    private EditText editTextEmail;
    private EditText editTextPassword;
    private Button buttonSignIn;
    private Button buttonSignUp;

    private FirebaseAuth mAuth;

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

        editTextEmail = findViewById(R.id.editTextEmail);
        editTextPassword = findViewById(R.id.editTextPassword);
        buttonSignIn = findViewById(R.id.buttonSignIn);
        buttonSignUp = findViewById(R.id.buttonSignUp);

        mAuth = FirebaseAuth.getInstance();

        buttonSignIn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                signIn(editTextEmail.getText().toString(), editTextPassword.getText().toString());
            }
        });

        buttonSignUp.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                createAccount(editTextEmail.getText().toString(), editTextPassword.getText().toString());
            }
        });
    }

    private void signIn(String email, String password) {
        mAuth.signInWithEmailAndPassword(email, password)
            .addOnCompleteListener(this, task -> {
                if (task.isSuccessful()) {
                    FirebaseUser user = mAuth.getCurrentUser();
                    Toast.makeText(MainActivity.this, "Login successful: " + user.getEmail(), Toast.LENGTH_SHORT).show();
                } else {
                    Toast.makeText(MainActivity.this, "Login failed.", Toast.LENGTH_SHORT).show();
                }
            });
    }

    private void createAccount(String email, String password) {
        mAuth.createUserWithEmailAndPassword(email, password)
            .addOnCompleteListener(this, task -> {
                if (task.isSuccessful()) {
                    FirebaseUser user = mAuth.getCurrentUser();
                    Toast.makeText(MainActivity.this, "Registration successful: " + user.getEmail(), Toast.LENGTH_SHORT).show();
                } else {
                    Toast.makeText(MainActivity.this, "Registration failed.", Toast.LENGTH_SHORT).show();
                }
            });
    }
}
    

6. Running and Testing the App

After adding all the code, run the app to test if the functionality works well. Check if both login and sign-up functions work properly. It is also important to provide appropriate feedback to users and handle errors when they occur.

7. Implementing Additional Features

After building the basic sign-up and login functions, you can consider additional features like:

• Email Verification: Set up email verification after registration to enhance security.
• Password Reset: Add a feature that allows users to reset their password if they forget it.
• Social Login: Implement authentication using social accounts like Google and Facebook.
• User Profile Management: Add functionality to modify and view user profiles after authentication.

8. Conclusion

In this course, we learned how to implement authentication features in Android apps using Java. We were able to easily apply email/password-based login and registration functions through the Firebase Authentication library. Consider using various authentication methods to enhance the security of your application.

9. References

• Android Developer Documentation
• Firebase Authentication Documentation
• Android Networking

Image processing is an essential part of Android app development. In particular, the Glide library plays a significant role in efficiently loading and displaying images of various resolutions. In this tutorial, we will learn how to load and cache images using the Glide library.

1. Overview of the Glide Library

Glide is an image loading and caching library developed by Google, capable of fetching images from complex URLs or loading images from the local file system. Glide provides powerful capabilities to handle edge cases and various image formats, making it very useful in image processing applications.

2. Setting Up Glide

To use Glide, you first need to add the library to your Gradle file. Open the build.gradle file of your project in Android Studio and add the following dependencies.

dependencies {
    implementation 'com.github.bumptech.glide:glide:4.12.0'
    annotationProcessor 'com.github.bumptech.glide:compiler:4.12.0'
}

After adding the above content, synchronize the Gradle file to include the Glide library in your project.

3. Basic Usage of Glide

The usage of Glide is very simple. By default, you can load an image into an ImageView like this.

import com.bumptech.glide.Glide;

ImageView imageView = findViewById(R.id.imageView);
Glide.with(this)
     .load("https://example.com/image.jpg")
     .into(imageView);

In the above code, Glide.with(this) retrieves the context of the current activity, and the .load() method is used to fetch the image. Finally, the .into() method is used to set the image into the ImageView.

4. Image Loading Options in Glide

Glide offers various image loading options. Here are some common options used frequently.

4.1. Resizing Images

You can resize the image to your desired dimensions while loading. The example below shows how to load an image resized to 100×100 pixels.

Glide.with(this)
     .load("https://example.com/image.jpg")
     .override(100, 100)
     .into(imageView);

4.2. Setting Placeholder and Error Images

You can set a placeholder image to display while the image is loading or an error image to show in case of a loading failure.

Glide.with(this)
     .load("https://example.com/image.jpg")
     .placeholder(R.drawable.placeholder)
     .error(R.drawable.error)
     .into(imageView);

4.3. Creating Circular Images

If you want to create a circular image using Glide, refer to the following example.

import com.bumptech.glide.load.resource.bitmap.CircleCrop;

Glide.with(this)
     .load("https://example.com/profile.jpg")
     .transform(new CircleCrop())
     .into(imageView);

5. Caching Mechanism of Glide

Glide automatically performs caching when loading images. It uses both memory and disk caching to optimize performance.

5.1. Memory Cache

Memory cache helps the application quickly access images within the range of memory. This reduces the response time while loading images.

5.2. Disk Cache

Disk cache allows images to be saved on the device’s storage media, enabling faster loading for subsequent identical requests. This helps reduce data usage and improve performance.

6. Advanced Features of Glide

In addition to basic image loading, Glide provides various advanced features. Here are a few of them.

6.1. GIF Support

Glide allows you to easily load GIF images. The code below demonstrates how to set a GIF image in an ImageView.

Glide.with(this)
     .asGif()
     .load("https://example.com/animation.gif")
     .into(imageView);

6.2. Implementing a Progress Bar

You can display a progress bar while the image is loading using Glide. The RequestListener of Glide can be used to handle loading states.

Glide.with(this)
     .load("https://example.com/image.jpg")
     .listener(new RequestListener() {
         @Override
         public boolean onLoadFailed(@Nullable GlideException e, Object model, Target target, boolean isFirstResource) {
             // Handle load failure
             return false;
         }

         @Override
         public boolean onResourceReady(Drawable resource, Object model, Target target, DataSource dataSource, boolean isFirstResource) {
             // Handle successful image load
             return false;
         }
     })
     .into(imageView);

6.3. Parameter Tuning

Glide provides capabilities to manage images more precisely using additional parameters. For example, you can preprocess each image before loading them.

Glide.with(this)
     .load("https://example.com/image.jpg")
     .apply(RequestOptions.bitmapTransform(new BlurTransformation(25, 3)))
     .into(imageView);

Conclusion

Glide is an excellent tool that makes image processing simple and efficient in Android applications. By utilizing memory and disk cache options, you can improve the overall performance of your app, while supporting various image formats and transformation features. We hope you learned how to use Glide through this tutorial and can apply it to your apps.

Additionally, you can find the documentation for Glide here.