How to resize/scale an ImageButton in Android

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/rl"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="10dp"
    tools:context=".MainActivity"
    android:background="#b1b3a9"
    >
    <!-- ImageButton with default size, no scaling -->
    <ImageButton
        android:id="@+id/ib"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/image_button2"
        />
    <!-- ImageButton scaled, width 100dp and height 50dp by XML -->
    <!-- ImageButton scale type fit center by XML -->
    <ImageButton
        android:id="@+id/ib2"
        android:layout_width="100dp"
        android:layout_height="50dp"
        android:src="@drawable/image_button2"
        android:layout_alignParentRight="true"
        android:scaleType="fitCenter"
        />
    <!-- ImageButton scaled, width 200dp and height 100dp by XML -->
    <!-- ImageButton scale type fit x y by XML -->
    <ImageButton
        android:id="@+id/ib3"
        android:layout_width="200dp"
        android:layout_height="100dp"
        android:src="@drawable/image_button2"
        android:layout_alignParentBottom="true"
        android:layout_alignParentLeft="true"
        android:scaleType="fitCenter"
        />
    <!-- ImageButton scaling programmatically in java code -->
    <ImageButton
        android:id="@+id/ib4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/image_button2"
        android:layout_alignParentRight="true"
        android:layout_alignParentBottom="true"
        />
</RelativeLayout>

package com.jigopost.resizebutton;

import android.os.Bundle;
import android.app.Activity;
import android.widget.ImageButton;
import android.widget.ImageView;
import android.widget.RelativeLayout;


public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Get the widgets reference from XML layout
        final RelativeLayout rl = (RelativeLayout) findViewById(R.id.rl);
        final ImageButton ib = (ImageButton) findViewById(R.id.ib);
        final ImageButton ib2 = (ImageButton) findViewById(R.id.ib2);
        final ImageButton ib3 = (ImageButton) findViewById(R.id.ib3);
        final ImageButton ib4 = (ImageButton) findViewById(R.id.ib4);

        // Get the last ImageButton's layout parameters
        RelativeLayout.LayoutParams params = (RelativeLayout.LayoutParams) ib4.getLayoutParams();

        // Set the height of this ImageButton
        params.height = 200;

        // Set the width of that ImageButton
        params.width = 350;

        // Apply the updated layout parameters to last ImageButton
        ib4.setLayoutParams(params);

        // Set the ImageButton image scale type for fourth ImageButton
        ib4.setScaleType(ImageView.ScaleType.FIT_XY);
   }
}