The problem was in taking the data from the user in the MovieReg_activity
and its solved by putting those two lines
EditText etmovie_name = (EditText)findViewById(R.id.etmovname);
movName= etmovie_name.getText().toString();
inside the button listener to be like this
public void onClick(View v) {
int x=0 ;
EditText etmovie_name = (EditText)findViewById(R.id.etmovname);
movName= etmovie_name.getText().toString();
movies.add(new movie(movName , dvdNo) );
String name3= movie.getName() ;
x++ ;
int size =movies.size() ;
Toast.makeText(MovieReg_activity.this, "no of movies added :"+size , Toast.LENGTH_SHORT).show();
}
});