Android studio java projects

How To Create New Java Class In Android Studio

In android development, the java class is commonly used to implement business logic processes such as database access, send emails, send short messages etc. We always use one java class to encapsulate some related functions.

So we can think java class as the Model role in the MVC pattern. This example will show you how to create a new java class in android studio, and we will create a SMSBean java class that will implement short message send and receives functions.

1.How To Create New Java Class In Android Studio.

1. Launch Android Studio, create a new project. You can read the article How To Create New Android Studio Project to learn more.
2. After that right-click the default package in the android studio Project View’s Android subview, then click the New —> Java Class menu item.
3. You can also click the New —> Package menu item to create a new package or sub-package under exist package. In this example, we create a sub-package model under the existing com.dev2qa.example package.
4. Then there will popup a dialog that will let you input java class-related information. Input class name SMSBean in the Name input text box, select Class in the Kind drop-down list, do not input any superclass, do not implement any interface. Input package name value such as com.dev2qa.example.model. Click the OK button.
5. After clicking the OK button, the java class SMSBean has been created successfully. We will add two methods in it, one is sendSMS(), the other is receiveSMS(), please see code comments for detail.

2. Java Class SMSBean Usage Example.

This example will use SMSBean as a short messages manager object, it has two methods sendSMS() and receiveSMS().

The user interface of this example is not complex, there will have two buttons on the screen one is used to send short messages, the other is used to receive short messages. When you click any of the two buttons, an AlertDialog will pop up showing some messages.

If you can not watch the above video, you can see it on the youtube URL https://youtu.be/VhM3qIQkuD8

So if you want to run this example, you should create a new activity and layout XML files to implement the user interface. You can read the below articles if you do not know how to create activity and use event listener.

Источник

Build Your First Android App in Java

1. Welcome!

In this codelab, you’ll learn how to build and run your first Android app in the Java programming language. (If you’re looking for the Kotlin version of this codelab, you can go here.)

What you must know already

This codelab is written for programmers and assumes that you know either the Java or Kotlin programming language. If you are an experienced programmer and adept at reading code, you will likely be able to follow this codelab, even if you don’t have much experience with Java.

What you’ll learn

• How to use Android Studio to build your app.
• How to run your app on a device or in the emulator.
• How to add interactive buttons.
• How to display a second screen when a button is pressed.

Use Android Studio and Java to write Android apps

You write Android apps in the Java programming language using an IDE called Android Studio. Based on JetBrains’ IntelliJ IDEA software, Android Studio is an IDE designed specifically for Android development.

Note: This version of the codelab requires Android Studio 3.6 or higher.

To work through this codelab, you will need a computer that can run Android Studio 3.6 or higher (or already has Android Studio 3.6 or higher installed).

2. Install Android Studio

Note: This version of the codelab requires Android Studio 3.6 or higher.

You can download Android Studio 3.6 from the Android Studio page.

Android Studio provides a complete IDE, including an advanced code editor and app templates. It also contains tools for development, debugging, testing, and performance that make it faster and easier to develop apps. You can use Android Studio to test your apps with a large range of preconfigured emulators, or on your own mobile device. You can also build production apps and publish apps on the Google Play store.

Note: Android Studio is continually being improved. For the latest information on system requirements and installation instructions, see the Android Studio download page.

Android Studio is available for computers running Windows or Linux, and for Macs running macOS. The OpenJDK (Java Development Kit) is bundled with Android Studio.

The installation is similar for all platforms. Any differences are noted below.

1. Navigate to the Android Studio download page and follow the instructions to download and install Android Studio.
2. Accept the default configurations for all steps, and ensure that all components are selected for installation.
3. After the install is complete, the setup wizard downloads and installs additional components, including the Android SDK. Be patient, because this process might take some time, depending on your internet speed.
4. When the installation completes, Android Studio starts, and you are ready to create your first project.

Troubleshooting: If you run into problems with your installation, see the Android Studio release notes or Troubleshoot Android Studio.

3. Task: Create your first project

In this step, you will create a new Android project for your first app. This simple app displays the string «Hello World» on the screen of an Android virtual or physical device.

Here’s what the finished app will look like:

What you’ll learn

• How to create a project in Android Studio.
• How to create an emulated Android device.
• How to run your app on the emulator.
• How to run your app on your own physical device, if you have one.

Step 1: Create a new project

1. Open Android Studio.
2. In the Welcome to Android Studio dialog, click Start a new Android Studio project.
3. Select Basic Activity (not the default). Click Next.
4. Give your application a name such as My First App.
5. Make sure the Language is set to Java.
6. Leave the defaults for the other fields.
7. Click Finish.

After these steps, Android Studio:

• Creates a folder for your Android Studio project called MyFirstApp. This is usually in a folder called AndroidStudioProjects below your home directory.
• Builds your project (this may take a few moments). Android Studio uses Gradle as its build system. You can follow the build progress at the bottom of the Android Studio window.
• Opens the code editor showing your project.

Step 2: Get your screen set up

When your project first opens in Android Studio, there may be a lot of windows and panes open. To make it easier to get to know Android Studio, here are some suggestions on how to customize the layout.

1. If there’s a Gradle window open on the right side, click on the minimize button (—) in the upper right corner to hide it.
2. Depending on the size of your screen, consider resizing the pane on the left showing the project folders to take up less space.

At this point, your screen should look a bit less cluttered, similar to the screenshot shown below.

Step 3: Explore the project structure and layout

The upper left of the Android Studio window should look similar to the following diagram:

Based on you selecting the Basic Activity template for your project, Android Studio has set up a number of files for you. You can look at the hierarchy of the files for your app in multiple ways, one is in Project view. Project view shows your files and folders structured in a way that is convenient for working with an Android project. (This does not always match the file hierarchy! To see the file hierarchy, choose the Project files view by clicking (3).)

1. Double-click the app (1) folder to expand the hierarchy of app files. (See (1) in the screenshot.)
2. If you click Project (2), you can hide or show the Project view. You might need to select View > Tool Windows to see this option.
3. The current Project view selection (3) is Project > Android.

In the Project > Android view you see three or four top-level folders below your app folder: manifests, java, java (generated) and res. You may not see java (generated) right away.

1. Expand the manifests folder.

This folder contains AndroidManifest.xml . This file describes all the components of your Android app and is read by the Android runtime system when your app is executed. 2. Expand the java folder. All your Java language files are organized here. The java folder contains three subfolders:

com.example.myfirstapp: This folder contains the Java source code files for your app.

com.example.myfirstapp (androidTest): This folder is where you would put your instrumented tests, which are tests that run on an Android device. It starts out with a skeleton test file.

com.example.myfirstapp (test): This folder is where you would put your unit tests. Unit tests don’t need an Android device to run. It starts out with a skeleton unit test file. 3. Expand the res folder. This folder contains all the resources for your app, including images, layout files, strings, icons, and styling. It includes these subfolders:

drawable: All your app’s images will be stored in this folder.

layout: This folder contains the UI layout files for your activities. Currently, your app has one activity that has a layout file called activity_main.xml . It also contains content_main.xml , fragment_first.xml , and fragment_second.xml .

menu: This folder contains XML files describing any menus in your app.

mipmap: This folder contains the launcher icons for your app.

navigation: This folder contains the navigation graph, which tells Android Studio how to navigate between different parts of your application.

values: This folder contains resources, such as strings and colors, used in your app.

Step 4: Create a virtual device (emulator)

In this task, you will use the Android Virtual Device (AVD) manager to create a virtual device (or emulator) that simulates the configuration for a particular type of Android device.

The first step is to create a configuration that describes the virtual device.

1. In Android Studio, select Tools >AVD Manager, or click the AVD Manager icon in the toolbar.
2. Click +Create Virtual Device. (If you have created a virtual device before, the window shows all of your existing devices and the +Create Virtual Device button is at the bottom.) The Select Hardware window shows a list of pre-configured hardware device definitions.
3. Choose a device definition, such as Pixel 2, and click Next. (For this codelab, it really doesn’t matter which device definition you pick).
4. In the System Image dialog, from the Recommended tab, choose the latest release. (This does matter.)
5. If a Download link is visible next to a latest release, it is not installed yet, and you need to download it first. If necessary, click the link to start the download, and click Next when it’s done. This may take a while depending on your connection speed.

Note: System images can take up a large amount of disk space, so just download what you need.

1. In the next dialog box, accept the defaults, and click Finish.

The AVD Manager now shows the virtual device you added.

1. If the Your Virtual Devices AVD Manager window is still open, go ahead and close it.

Step 5: Run your app on your new emulator

1. In Android Studio, select Run > Run ‘app’ or click the Run icon in the toolbar. The icon will change when your app is already running.

If you get a dialog box stating «Instant Run requires that the platform corresponding to your target device (Android N. ) is installed» go ahead and click Install and continue.

1. In Run > Select Device, under Available devices, select the virtual device that you just configured. This menu also appears in the toolbar.

The emulator starts and boots just like a physical device. Depending on the speed of your computer, this may take a while. You can look in the small horizontal status bar at the very bottom of Android Studio for messages to see the progress.

Messages that might appear briefly in the status bar

Gradle build running

Waiting for target device to come on line

Источник