Basic Event Handling in Android

MainActivity.java

package com.example.mac.testapp;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends Activity {

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

        final EditText editText = (EditText) findViewById(R.id.text1) ; /*this will contain the name */
        final TextView text2 = (TextView) findViewById(R.id.text2) ; /*this will contain the welcome message */
        final Button button = (Button) findViewById(R.id.button) ;


        /*This is an example of using Event Listeners in Android */
        button.setOnClickListener( new Button.OnClickListener() {
            public void onClick(View view){
                Log.i(Constants.INFO, "Id of the view is "+ (view.getId() == R.id.button)) ;
                final String name  = editText.getText().toString() ;
                if(name.trim().isEmpty()){
                    /*TODO: give an error on the UI. Name cannot be empty */
                    editText.setError("You have to enter a name");
                    return;
                }
                final String message = "Hello "+name+" !" ;
                text2.setText(message);

            }
        } );

    }
}