Textview Gravity not working properly in android

What's wrong with my code, I'm trying to display my TextView named "invalid", in different locations (left,right,center), but the gravity (left,right,center) won't work!

My text.xml is

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="20dp" >

    <EditText 
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/etext"
        android:hint="@string/comment"
        android:inputType="textPassword"/>

    <LinearLayout 
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:weightSum="100">
        <Button
            android:id="@+id/button1"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:text="@string/button" 
            android:layout_weight="25"/>

        <ToggleButton
            android:id="@+id/toggleButton1"
            android:layout_width="fill_parent"
            android:layout_height="40dp"
            android:text="ToggleButton" 
            android:layout_weight="75"
            android:checked="true"
            android:paddingLeft="15dp"/>
    </LinearLayout>

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/invalid"
        android:layout_gravity="center"
        android:gravity="center" />
</LinearLayout>

My TextPlay.java is

public class TextPlay extends Activity {
    Button button;
    ToggleButton tbutton;
    TextView tview;
    EditText et;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.text);
        button = (Button) findViewById(R.id.button1);
        tbutton = (ToggleButton) findViewById(R.id.toggleButton1);
        tview = (TextView) findViewById(R.id.textView1);
        et = (EditText) findViewById(R.id.etext);
        tbutton.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                if (tbutton.isChecked()) {
                    et.setInputType(InputType.TYPE_CLASS_TEXT | InputType.TYPE_TEXT_VARIATION_PASSWORD);
                } else {
                    et.setInputType(InputType.TYPE_TEXT_VARIATION_PASSWORD);
                }
            }
        });
        button.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                String input = et.getText().toString();
                System.out.println(input);
                if (input.contentEquals("left")) {
                    tview.setGravity(Gravity.LEFT);
                } else if (input.contentEquals("right")) {
                    System.out.println("inside right");
                    tview.setGravity(Gravity.RIGHT);
                } else if (input.contentEquals("right")) {
                    tview.setGravity(Gravity.CENTER);
                }
            }
        });
    }
}

You set this text view a width of "wrap_content" it means, what ever the text is, the view take the size of the text.

and in the LinearLayout , the default gravity (used here) is 'center'

you should try this :

<TextView
android:id="@+id/textView1"
android:layout_width="match_parent"   <= change this
android:layout_height="wrap_content"
android:text="@string/invalid"
android:gravity="center"   <= then this gravity will be taken into account
/>