import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    TextView tv = null;
    Button bouton;

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

        tv = (TextView) findViewById(R.id.tv1);

        Button bt = (Button) findViewById(R.id.bt2);
        bt.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View view) {
                tv.setText("Vous avez utilisé un listener !");
            }
        });
    }

    public void cliqueBouton1(View view)
    {
        tv.setText("Vous avez utilisé la méthode onClick !");
    }
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:orientation="vertical">

        <Button
            android:id="@+id/bt1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:onClick="cliqueBouton1"
            android:text="Bouton 1" />

        <Button
            android:id="@+id/bt2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:text="Bouton 2" />

        <TextView
            android:id="@+id/tv1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:text="Vous n'avez cliqué sur aucun bouton" />

    </LinearLayout>
    
</RelativeLayout>