вам не хватает разных вещей, во-первых, ScrollView не имеет мер, установите его с помощью LayoutParams.FILL_PARENT или WRAP_CONTENT, во-вторых;это TextView1 неуместно, поэтому TextView2, установите позицию TextView1 с lay.addRule (RelativeLayout.ALIGN_PARENT_TOP, RelativeLayout.TRUE);
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ScrollView sv = new ScrollView(this);
RelativeLayout ll = new RelativeLayout(this);
ll.setId(99);
sv.addView(ll, new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT));
TextView tv = new TextView(this);
tv.setText("txt1");
tv.setId(1);
TextView tv2 = new TextView(this);
tv2.setText("txt2");
tv2.setId(2);
RelativeLayout.LayoutParams lay = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT);
lay.addRule(RelativeLayout.ALIGN_PARENT_TOP, RelativeLayout.TRUE);
ll.addView(tv, lay);
RelativeLayout.LayoutParams p = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT);
p.addRule(RelativeLayout.ALIGN_BOTTOM, tv.getId());
ll.addView(tv2, p);
this.setContentView(sv);};