Type writer style append text view

MainActivity.java

import android.os.Bundle;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    private Handler handler;
    private int idx = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        TextView textView = (TextView) findViewById(R.id.tv);

        final String STRING = "Hello Android";

        /*pass in 3 params:
        * 1) the string you wish to display
        * 2) the text view you wish to display the string in
        * 3) the delay time for appending the text view with the next character in
        * the string...
        */
        typeWriter(STRING, textView, 300);
    }


    public void typeWriter(String string, final TextView textView, final int DELAY) {

        final char[] ca = string.toCharArray();
        final int max = ca.length;
        handler = new Handler();

        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                textView.append(String.format("%c", ca[idx]));
                idx++;
                if (idx < max) handler.postDelayed(this, DELAY);
            }
        };

        handler.post(runnable);
    }
}