Using below code I have created Digital clock app in android. Android digital clock is used to show time in android app. In android, digitalclock is the sub class of TextView class. Here below code example will help you create Digital Clock function in android.

Srep(1)- activity_main.xml

<RelativeLayout xmlns:androclass="http://schemas.android.com/apk/res/android"  
    xmlns:tools="http://schemas.android.com/tools"  
    android:layout_width="match_parent"  
    android:layout_height="match_parent"  
    tools:context=".MainActivity" >  

    <AnalogClock  
        android:id="@+id/analogClock1"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:layout_alignParentTop="true"  
        android:layout_centerHorizontal="true"  
        android:layout_marginTop="22dp" />  

    <DigitalClock  
        android:id="@+id/digitalClock1"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:layout_below="@+id/analogClock1"  
        android:layout_centerHorizontal="true"  
        android:layout_marginTop="81dp"  
        android:text="DigitalClock" />  

</RelativeLayout>  

Step(2)- MainActivity.class

public class MainActivity extends Activity {  

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

    @Override  
    public boolean onCreateOptionsMenu(Menu menu) {  
        getMenuInflater().inflate(R.menu.activity_main, menu);  
        return true;  
    }  
}