Button to go back to the previous page

I want to make a button that allow user to go back to the previous page when click. Just work like the physical back button on the android device. What should I add to the java file?

here is the code(xml):

<Button
        android:id="@+id/button00"
        android:layout_width="80dp"
        android:layout_height="40dp"
        android:layout_marginTop="5dp"
        android:layout_marginBottom="5dp"
        android:layout_marginLeft="10dp"
        android:text="@string/st_pp"
        android:textColor="#01646d"
        android:background="#fef200"/>

here is the code(java):

bn00.setOnClickListener(new OnClickListener(){

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                Intent it1 = new Intent(getApplicationContext(), Main.class);
                startActivity(it1);
            }

        });

To go back to previous activity use finish() method. But note that previous activity not contains finish() while you call current activity.

Code :

bn00.setOnClickListener(new OnClickListener(){

            @Override
            public void onClick(View arg0) {

                finish();
            }

        });

Using above code you can go to your previous activity. You can also call finish() in onKeyDown() method like..

@Override
public boolean onKeyDown(int keyCode, KeyEvent event)  {
    if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
       finish();
        return true;
    }

    return super.onKeyDown(keyCode, event);
}