How to build a simple Android app

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Activity Lifecycle

package cs.ecl.mobile.android.simple;

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

public class ActivityLifecycle extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Toast.makeText(this, " onCreate", Toast.LENGTH_SHORT).show();
    }

    @Override
    protected void onStart() {
        super.onStart();
        Toast.makeText(this, " onStart", Toast.LENGTH_SHORT).show();
    }

    @Override
    protected void onResume() {
        super.onResume();
        Toast.makeText(this, " onResume", Toast.LENGTH_SHORT).show();
    }

    @Override
    protected void onRestart() {
        super.onRestart();
        Toast.makeText(this, " onRestart", Toast.LENGTH_SHORT).show();
    }

    @Override
    protected void onPause() {
        Toast.makeText(this, "onPause", Toast.LENGTH_SHORT).show();
        super.onPause();
    }

    @Override
    protected void onStop() {
        Toast.makeText(this, "onStop", Toast.LENGTH_SHORT).show();
        super.onStop();
    }

    @Override
    protected void onDestroy() {
        Toast.makeText(this, "onDestroy", Toast.LENGTH_SHORT).show();
        super.onDestroy();
    }
}

Run the app and try to understand the sequences of message based on diagram from android developers site

The entire source code for this application could be found at: sample that illustrates the activity