Hello Android

public class HelloWorldActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
}

Notice that the class is based on the Activity class. An Activity is a single application entity that is used to perform actions. An application may have many separate activities, but the user interacts with them one at a time. The onCreate() method will be called by the Android system when your Activity starts - it is where you should perform all initialization and UI setup.

Now we have to modify this file to display a hello world message so modify the file this way:

First we are required to add a package; import android.widget.TextView as in:

package myexample.main;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;

public class HelloWorldActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
TextView tv = new TextView(this);
//Set a text into view
tv.setText("Hello This is My First Android Application :)");
//set the view into activity view container
setContentView(tv);
}
}

An Android user interface is composed of hierarchies of objects called Views. A View is a drawable object used as an element in your UI layout, such as a button, image, or (in this case) a text label. Each of these objects are a subclass of the View class and the subclass that handles text is TextView.

In this change, you create a TextView with the class constructor, which accepts an Android Context instance as its parameter. A Context is a handle to the system; it provides services like resolving resources, obtaining access to databases and preferences, and so on. The Activity class inherits from Context, and because your HelloAndroid class is a subclass of Activity, it is also a Context. So, you can pass this as your Context reference to the TextView.

Next, you define the text content with setText().

Finally, you pass the TextView to setContentView() in order to display it as the content for the Activity UI. If your Activity doesn't call this method, then no UI is present and the system will display a blank screen.

Now it's time to run our application:

Go to the Window - > Android SDK and AVD Manager.

In that window click New; give any name for ex :MyAndroid.

At SD Card give the size 256, Skin select HVGA.

Click Create AVD



Now it's time to run. Right-click on your project and choose:

Run As -> Android Application

The first time it will require a little time to configure, so wait until you get a window.

Now click on all application from the Emulator.



On all application you will get your hello world application too.



Click on it and see the result.



Thank you!