MainActivity.java

// See: https://imgur.com/gafDVW5

package com.example.mark.myapplication;

import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.RelativeLayout;
import android.widget.Button;
import android.graphics.Color;
import android.widget.EditText;
import android.content.res.Resources;
import android.util.TypedValue;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        RelativeLayout marksLayout = new RelativeLayout(this);
        marksLayout.setBackgroundColor(Color.GREEN);

        Button redButton = new Button(this);
        redButton.setText("Click Me");
        redButton.setBackgroundColor(Color.RED);
        redButton.setId(1);

        EditText username = new EditText(this);
        username.setId(2);

        RelativeLayout.LayoutParams buttonDetails = new RelativeLayout.LayoutParams(
                RelativeLayout.LayoutParams.WRAP_CONTENT,
                RelativeLayout.LayoutParams.WRAP_CONTENT
        );
        RelativeLayout.LayoutParams usernameDetails = new RelativeLayout.LayoutParams(
                RelativeLayout.LayoutParams.WRAP_CONTENT,
                RelativeLayout.LayoutParams.WRAP_CONTENT
        );

        usernameDetails.addRule(RelativeLayout.ABOVE, redButton.getId());
        usernameDetails.addRule(RelativeLayout.CENTER_HORIZONTAL);
        usernameDetails.setMargins(0, 0, 0, 50);

        buttonDetails.addRule(RelativeLayout.CENTER_HORIZONTAL);
        buttonDetails.addRule(RelativeLayout.CENTER_VERTICAL);

        Resources r = getResources();
        int px = (int)TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 200, r.getDisplayMetrics());
        username.setWidth(px);

        marksLayout.addView(redButton, buttonDetails);
        marksLayout.addView(username, usernameDetails);
        setContentView(marksLayout);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}