Android is an operating system based on Linux with a Java programming interface. It provides tools, e.g. a compiler, debugger and a device emulator as well as its own Java Virtual machine (Dalvik).

Android is created by the Open Handset Alliance which is lead by Google.

Android uses a special Java virtual machine (Dalvik) which is based on the Apache Harmony Java implementation. Dalvik uses a special Bytecode so that you have to use the Android compiler to create this special byte-code.

Android supports 2-D and 3-D graphics using the OpenGL libraries and supports data storage in a SQLLite database.

For development Google provides the Android Development Tools (ADT) for Eclipse to develop Android applications.

An Android application consists out of the following parts:

An Android application is described the file "AndroidManifest.xml". This files contains all classes of the application and the required permissions for the application, e.g. if the application requires network access. "AndroidManifest.xml" can be thought as the deployment descriptor for an Android application.

Use the update manager of Eclipse to install all available plugins for the Android Development Tools (ADT) from the URL https://dl-ssl.google.com/android/eclipse/ . See Using the Eclipse update manager for details on how to use the update manager and how to install new plugins.

Download the Android SDK from the Android homepage under Android Homepage .

The download contains a zip file which you can extract to any place in your file system, e.g. I placed it under "c:\android-sdk-windows" .

In Eclipse open the Preferences dialog via Windows -> Preferences. Select Android and maintain the installation path of the Android SDK.

Select now Window -> Android SDK and AVD Manager from the menu.

Select available packages and select everything expect the older version of the SDK.

Press "Install selected" and confirm the license for all package.

After the installation restart Eclipse.

You need to define a device which can be used for emulation. Press the device manager button, press "New" and maintain the following.

Press "Create AVD".

To test if you setup is correct, eelect your device and press "Start".

After (a long time) your device should be started.

. Select File -> New -> Other -> Android -> Android Project and create the Android project "de.vogella.android.first" Maintain the following.

Press "Finish".

This should create the following directory structure.

R.java is a generated class which contains the text and the UI elements. Please do not try to modify this class manually.

Select main.xml and open the editor via double-click. The result should look like the following.

From the "Views" bar, drag in an "EditText" and three "Buttons". The result should look like the following.

Select "string.xml" and press "Add".

Select color and maintain "white" as the name and "#FFFFFF" as the value.

Go back to "main.xml", select the complete widget and use the Properties view to set the background to this attribute.

Change your code in "Hello.java" to the following.

				package de.vogella.android.first;import android.app.Activity;import android.os.Bundle;import android.view.View;import android.widget.EditText;public class Hello extends Activity {	private EditText text;	/** Called when the activity is first created. */	@Override	public void onCreate(Bundle savedInstanceState) {		super.onCreate(savedInstanceState);		setContentView(R.layout.main); // bind the layout to the activity		text = (EditText) findViewById(R.id.EditText01);		text.setText("No button pressed");	}	// Will be connected with the buttons via XML	public void myClickHandler(View view) {		switch (view.getId()) {		case R.id.Button01:			text.setText("Button 1 was clicked");			break;		case R.id.Button02:			text.setText("Button 2 was clicked");			break;		case R.id.Button03:			text.setText("Button 3 was clicked");			break;		}	}}			

Open again main.xml and select your first button. Via the property view assign the method "myClickHandlerButton" to the "on Click" property of the first button.

Assign "myClickHandlerButton" to the other buttons.

The resulting main.xml should look like the following.

				<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:background="@color/white"><TextView      android:layout_width="fill_parent"     android:layout_height="wrap_content"     android:text="@string/hello"    /><EditText android:text="@+id/EditText01" android:id="@+id/EditText01" android:layout_width="wrap_content" android:layout_height="wrap_content"></EditText><Button android:text="@+id/Button01" android:id="@+id/Button01" android:layout_width="wrap_content" android:layout_height="wrap_content" android:onClick="myClickHandler"></Button><Button android:text="@+id/Button02" android:id="@+id/Button02" android:layout_width="wrap_content" android:layout_height="wrap_content" android:onClick="myClickHandler"></Button><Button android:text="@+id/Button03" android:id="@+id/Button03" android:layout_width="wrap_content" android:layout_height="wrap_content" android:onClick="myClickHandler"></Button></LinearLayout>			

To start the Android Application, select your project, right click on it, Run-As-> Android Application

You should get the following result.

If you press the Home button you can also select your application.

You can see the log (including System.out.print() statements) via the LogCat view.

The file explorer allows to see the files on the android simulator.

Android allows to access the network via the the java.net.URL class.

To set the proxy you can use the class Settings. For example you could add the following line to your onCreate method in your activity.

				Settings.System.putString(getContentResolver(), Settings.System.HTTP_PROXY, "myproxy:8080");			

You also have to give your application the right to change the settings "android.permission.WRITE_SETTINGS" in "AndroidManifest.xml".

Create the project "de.vogella.android.network.html". Add the following elements to your activity:

Create the following code to read a webpage and show the HTML code in the TextView.

This example also demonstrate the usage of Android preferences to store user data. The URL which the user has typed is stored in the preferences in the method onPause(). This method is called whenever the Activity is send into the background.

				package de.vogella.android.network.html;import java.io.BufferedReader;import java.io.InputStreamReader;import java.net.URL;import android.app.Activity;import android.content.SharedPreferences;import android.content.SharedPreferences.Editor;import android.os.Bundle;import android.view.View;import android.widget.EditText;import android.widget.TextView;public class ReadWebpage extends Activity {	private static final String PREFERENCES = "PREFERENCES";	private static final String URL = "url";	private String lastUrl;	private EditText urlText;	private TextView textView;	/** Called when the activity is first created. */	@Override	public void onCreate(Bundle savedInstanceState) {		super.onCreate(savedInstanceState);		setContentView(R.layout.main);		urlText = (EditText) findViewById(R.id.address);		textView = (TextView) findViewById(R.id.pagetext);		loadPreferences();		urlText.setText(lastUrl);	}		/**	 * Demonstrates loading of preferences The last value in the URL string will	 * be loaded	 */	private void loadPreferences() {		SharedPreferences preferences = getSharedPreferences(PREFERENCES,				Activity.MODE_PRIVATE);		// Set this to the Google Homepage		lastUrl = preferences.getString(URL, "http://209.85.229.147");	}	@Override	protected void onPause() {		super.onPause();		SharedPreferences preferences = getSharedPreferences(PREFERENCES,				Activity.MODE_PRIVATE);		Editor preferenceEditor = preferences.edit();		preferenceEditor.putString(URL, urlText.getText().toString());		// You have to commit otherwise the changes will not be remembered		preferenceEditor.commit();	}		// Will be connected with the buttons via XML	public void myClickHandler(View view) {		switch (view.getId()) {		case R.id.ReadWebPage:			try {				textView.setText("");				// Perform action on click				URL url = new URL(urlText.getText().toString());				// Get the response				BufferedReader rd = new BufferedReader(						new InputStreamReader(url.openStream()));				String line = "";				while ((line = rd.readLine()) != null) {					textView.append(line);				}			}			catch (Exception e) {				System.out.println("Nay, did not work");				textView.setText(e.getMessage());			}			break;		}	}}			

Assign the handler "buttonHandler" to the button in the property "on Click". via your XML.

ContentProvider are used to provide data from an application to another. ContentProvider do not store the data but provide the interface for other applications to access the data.

The following example will use an existing context provider from "Contacts".

Start the contacts application and create a few contacts.

Create a new Android project "de.vogella.android.contentprovider" with the activity "ContactsView".

Rename the id of the the existing TextView from the example wizard to "contactview". Delete the default text. Also change the layout_height to "fill_parent".

The resulting main.xml should look like the following.

				<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"	android:orientation="vertical" android:layout_width="fill_parent"	android:layout_height="fill_parent">	<TextView android:layout_width="fill_parent"		android:layout_height="fill_parent" android:id="@+id/contactview" /></LinearLayout>			

In Application.xml add the Permission that the application can use "android.permission.READ_CONTACTS".

Change now your coding of your activity.

				package de.vogella.android.contentprovider;import android.app.Activity;import android.database.Cursor;import android.os.Bundle;import android.provider.ContactsContract.Contacts;import android.widget.TextView;public class ContactsView extends Activity {	/** Called when the activity is first created. */	@Override	public void onCreate(Bundle savedInstanceState) {		super.onCreate(savedInstanceState);		setContentView(R.layout.main);		TextView contactView = (TextView) findViewById(R.id.contactview);		Cursor cursor = getContentResolver().query(Contacts.CONTENT_URI, null, null, null, null);		while(cursor.moveToNext()){			String displayName = cursor.getString(cursor.getColumnIndex(Contacts.DISPLAY_NAME));			contactView.append("Name: ");			contactView.append(displayName);			contactView.append("\n");		}	}}			

You can access your Android emulator also via the console. Open a shell, switch to your "android-sdk" installation directory into the folder "tools".

Start the shell via the command "adb shell".

The emulator console lets you dynamically access your simulated device. Use "telnet localhost 5554" to conntect to your simulated device. To exit the console session, use the command "quit" or "exit".

For example you can set your geolocation in the emulator via "geo fix -121.45356 46.51119 4392"

For more information on the emulator console please see Emulator Console manual

You can uninstall an android application via the shell. Switch the the data/app directory (cd /data/app) and simply delete your android application.

Create a new device which supports the Google API's.

Create a new project "de.vogella.android.locationapi". Make sure to select the Google API

Add the following permissions to your application in Android.xml.

You need to add the Google maps library to your application. Open Android.xml, tab Application and add a "Uses library".

Define your view layout like the following.

				<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:id="@+id/mainlayout"    android:orientation="vertical"    android:layout_width="fill_parent"    android:layout_height="fill_parent" >    <com.google.android.maps.MapView        android:id="@+id/mapview"        android:layout_width="fill_parent"        android:layout_height="fill_parent"        android:clickable="true"        android:apiKey="Your Maps API Key"    /></RelativeLayout>			

Create the following activity. This activity use an LocationListner to update the map with the current location.

				package de.vogella.android.locationapi;import android.content.Context;import android.location.Location;import android.location.LocationListener;import android.location.LocationManager;import android.os.Bundle;import android.widget.RelativeLayout;import android.widget.ZoomControls;import com.google.android.maps.GeoPoint;import com.google.android.maps.MapActivity;import com.google.android.maps.MapController;import com.google.android.maps.MapView;public class CurrentLocation extends MapActivity {	private MapController mapController;	private MapView mapView;	private LocationManager locationManager;	public void onCreate(Bundle bundle) {		super.onCreate(bundle);		setContentView(R.layout.main); // bind the layout to the activity		// create a map view		RelativeLayout linearLayout = (RelativeLayout) findViewById(R.id.mainlayout);		mapView = (MapView) findViewById(R.id.mapview);		ZoomControls mZoom = (ZoomControls) mapView.getZoomControls();		linearLayout.addView(mZoom);		mapController = mapView.getController();		// Zoon 1 is world view				mapController.setZoom(14);		locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);		locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0,				0, new GeoUpdateHandler());	}	@Override	protected boolean isRouteDisplayed() {		return false;	}	public class GeoUpdateHandler implements LocationListener {		@Override		public void onLocationChanged(Location location) {			int lat = (int) (location.getLatitude() * 1E6);			int lng = (int) (location.getLongitude() * 1E6);			GeoPoint point = new GeoPoint(lat, lng);			mapController.setCenter(point);//			setContentView(mapView);		}		@Override		public void onProviderDisabled(String provider) {		}		@Override		public void onProviderEnabled(String provider) {		}		@Override		public void onStatusChanged(String provider, int status, Bundle extras) {		}	}}			

Run and test your application. You should be able to zoon in and out. Use Emulator console to send geo-coordinates to your device for example

				geo fix 13.24 52.31			

http://www.vogella.de/code/codeeclipse.html Source Code of Examples

Android Homepage

Android Developer Homepage

Android Issues / Bugs

Android Market

SQL light database homepage

Content Provider Tutorial by Google

Notepad Tutorial from Google

http://www.ibm.com/developerworks/opensource/library/os-android-networking/index.html Networking with Android from Frank Ableson

http://www.ibm.com/developerworks/opensource/library/os-android-sensor/index.html Androids Sensors from Frank Ableson

http://www.ibm.com/developerworks/opensource/library/x-android/index.html Android and XML from Michael Galpin

Eclipse.org Homepage

Articles about Java, Eclipse and Webdevelopment from www.vogella.de

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Download "Eclipse IDE for Java Developers" from the website Eclipse Downloads and unpack it to a directory. This is sufficient for Eclipse to be used; no additional installation procedure is required.

To start Eclipse double-click on the file eclipse.exe in your installation directory.

The system will prompt you for a workspace. The workspace is the place there you store your Java projects (more on workspaces later). Select a suitable (empty) directory and press Ok.

Eclipse will start and show the Welcome page.

Close the welcome page by press in little x besides the Welcome.

The workspace is the physical location (file path) you are working in. You can choose the workspace during startup of eclipse or via the menu (File-> Switch Workspace-> Others).

All your projects, sources files, images and other artifacts will be stored and saved in your workspace.

A perspective is a visual container for a set of views and editors.

You can change the layout within a perspective (close / open views, editors, change the size, change the position, etc.)

Eclipse allow you to switch to another perspective via the menu Window->Open Perspective -> Other.

For Java development you usually use the "Java Perspective".

A view is typically used to navigate a hierarchy of information or to open an editor. Changes in a view are directly applied.

Editors are used to modify elements. Editors can have code completion, undo / redo, etc. To apply the changes in an editor to the underlying resources, e.g. Java source file, you usually have to save.

Select from the menu File -> New-> Java project. Maintain "de.vogella.eclipse.ide.first" as the project name. Select "Create separate source and output folders".

Press finish to create the project. A new project is created and displayed as a folder. Open the folder "de.vogella.eclipse.ide.first"

Create now a package. A good convention is to use the same name for the top package as the project. Create therefore the package "de.vogella.eclipse.ide.first".

Select the folder src, right mouse click on it and select New -> Package.

Right click on your package and select New -> Class

Create MyFirstClass, select the flag "public static void main (String[] args)"

Maintain the following code.

				package de.vogella.eclipse.ide.first;public class MyFirstClass {	public static void main(String[] args) {		System.out.println("Hello Eclipse!");	}}			

Now run your code. Right click on your Java class and select Run-as-> Java application

Finished! You should see the output in the console.

To run your Java program outside of Eclipse you need to export it as a jar file. Select your project, right click on it and select "Export".

Select JAR file, select next. Select your project and maintain the export destination and a name for the jar file. I named it "myprogram.jar".

Press finish. This will create a jar file in your select output directory.

Open a command shell, e.g. under Microsoft Windows select Start -> Run and type in cmd. This should open a consle.

Switch to your output directory, e.g. by typing cd path, e.g. if you jar is located in "c:\temp" type "cd c:\temp".

To run this program you need to include the jar file into your classpath. See Classpath and Java JAR Files for details.

				java -classpath myprogram.jar de.vogella.eclipse.ide.first.MyFirstClass			

Congratulations! You created your first Java project, a package a tiny Java program and you ran this program inside Eclipse and outside

The content assistant allows you to get input help in an editor. It can be invoked by CTRL + Space.

For example type syso and then press [Ctrl + Space] and it will be replaced by System.out.println(""). Or if you have an object, e.g. Person P and need to see the methods of this object you can type p. (or press CTRL + Space) which activates also the content assist.

Whenever there is a problem Eclipse will underline the problematic place in the coding. Select this and press (Ctrl+1)

For example type "myBoolean = true;" If myBoolean is not yet defined, Eclipse will highlight it as an error. Select the variable and press "Ctrn+1", then Eclipse will suggest to create a field or local variable.

Quick Fix is extremely powerful, it allows you to create new local / field variables, new methods, classes, put try and catch around your exceptions, assign a statement to a variable etc.

The following describes how to add external jars to your project.

The following assumes you have a jar available.

Create a new Java project "de.vogella.eclipse.ide.jars". Create a new folder called "lib" (or use your existing folder) by right click on your project and selecting New -> Folder

From the menu select File -> Import -> File system. Select your jar and select the folder lib as target.

Select your project, right mouse click and select properties. Under libraries select "Add JARs".

The following example shows how the result would look like if junit-4.4.jar would be added to a project.

To browse the source of a type contained in library you can attach a source archive or source folder to this library. The editor will then show the source instead of a the decompiled code. Setting the source attachment also allows source level stepping with the debugger.

The Source Attachment dialog can be reached via:

Open the Java Build Path page of a project (Projects > Properties > Java Build Path). On the Libraries page expand the library's node and select the Source attachment attribute and press Edit

Maintain the location to the source attachement.

In the Location path field, enter the path of an archive or a folder containing the source.

Download the javadoc of the jar and put it somewhere in your filesystem.

Open the Java Build Path page of a project (Projects > Properties > Java Build Path). On the Libraries page expand the library's node and select the Javadoc location attribute and press Edit

Maintain the location to the api.

Eclipse provides functionality via so-called features (which contain plugins). Eclipse 3.5 contains a Software Update Manager which allows you to update existing plugins and to install new plugins.

To update your existing installation select the menu Help -> Check for Updates. The system will verify if for the installed plugins updates are available or not.

To install new functionality, select Help-> Install New Software.

Select from the list a update site from which you would like to install new software. For example if you want to install new plugins from Galileo select the Galileo Update Site.

To add a new update site select, press the button "Add" and input the URL. This will then make this update site available and will allow you to install software from this site.

If you’re using Plugins where no Software Site is available, then you can use the Dropins folder in your Eclipse installation directory.

To do this put the plugin into Eclipse "dropins" folder and restart Eclipse. Eclipse should detect the new plugin and install it for you.

The problems view displays problems in your projects. You can open it via Windows -> Show View -> Problems

You can configure the problems view, e.g. if you only want to display the problems from the current selected project, select "Configure Contents".

Eclipse allows to set semicolons (and other elements) automatically.

Eclipse allows to format the source code and to organize the imports at save.

If you use // TODO in the coding this indicates a task for eclipse and you find it in the task view of Eclipse.

For more advanced tasks you can use Eclipse Mylyn Tutorial .

A common problem in Eclipse is that your data in your workspace grows and therefore your workspace is not well structured anymore. You can use working sets to organize your displayed projects / data. To setup your working set select in the Package Explorer -> Show -> Working Sets.

Press new on the following dialog to create a working set.

On the following dialog select java, select the source folder you would like to see and give it a name. You can now easily display only the files you want to see.

The package explorer allows to display the associated file from the current selected editor. Example: if you working on foo.java and you change in the editor to bar.java then the display in the package explorer will change.

To activate this press "Link with Editor".

If you have to type frequently the same code / part of the d0cument you can maintain templates which can be activate via autocomplete (Ctrl + Space).

For example lets assume you are frequently creating "public void name(){}" methods. You could define a template which creates the method body for you.

To create a template for this select the menu Window->Preferences and Open Java -> Editor -> Templates

Press New. Create the following template. ${cursor} indicates that the cursor should be placed at this position after applying the template.

This this example the name "npm" is your keyword.

Now every time you type the keyword in the Java editor and press Ctrl+Space the system will replace your text with your template.

http://www.vogella.de/code/codeeclipse.html Source Code of Examples

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Articles about Java, Eclipse and Webdevelopment from www.vogella.de

Articles about Eclipse development from www.vogella.de

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