activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/txTexto"
        android:textSize="30sp"
        android:layout_margin="16dp"/>

</LinearLayout>

MainActivity.java

public class MainActivity extends AppCompatActivity {

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

        exibe("Hello World!");

    }

    private void exibe(String texto){
        TextView textView = (TextView) findViewById(R.id.txTexto);
        textView.setText(texto);
    }

    private void exibe(int numero){
        exibe(String.valueOf(numero));
    }

    private void exibe(double numero){
        exibe(String.valueOf(numero));
    }

    private void exibe(float numero){
        exibe(String.valueOf(numero));
    }

    private void exibe(char letra){
        exibe(String.valueOf(letra));
    }

    private void exibe(boolean condicao){
        exibe(String.valueOf(condicao));
    }
}