a basic Activity class in Android

create:
a TextBox (EditText)
two radio button grouped within a RadioGroup
a button.

e.g. main.xml

<?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"     > <EditText     android:id="@+id/txtCount"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:editable="false"/>     <RadioGroup android:layout_width="wrap_content" android:layout_height="wrap_content" android:orientation="horizontal">         <RadioButton     android:id="@+id/radioUp"     android:text="@string/radioUpLabel"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:checked="true"/>     <RadioButton     android:id="@+id/radioDown"     android:text="@string/radioDownLabel"     android:layout_width="wrap_content"     android:layout_height="wrap_content"/> </RadioGroup> <Button android:id="@+id/btnCount" android:text="@string/btnCountLabel" android:layout_width="wrap_content" android:layout_height="wrap_content"/> </LinearLayout>

The main Activity class:- CounterDemo

package com.test; import android.app.Activity; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.EditText; import android.widget.RadioButton; public class CounterDemo extends Activity implements OnClickListener{            private Button btnCount;     private EditText txtCount;     private RadioButton radioUp;     private RadioButton radioDown;     private int count = 0; // Initial count         @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.main);                 radioUp = (RadioButton)findViewById(R.id.radioUp);         radioDown = (RadioButton)findViewById(R.id.radioDown);                 txtCount = (EditText)findViewById(R.id.txtCount);         txtCount.setText(String.valueOf(count));                 // Get the reference to the Button view         btnCount = (Button)findViewById(R.id.btnCount);         btnCount.setOnClickListener(this);               }        @Override        public void onClick(View arg0) {               if(radioUp.isChecked()){                      count++;               } else {                      count--;               }               txtCount.setText(String.valueOf(count));                      } }