Google Android - это несложно

Код: Выделить всё

package nightsun.manual;

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 implements View.OnClickListener {
    TextView textView;
    Button button;
    Button button2;
    Button button3;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textView = (TextView) findViewById(R.id.textView);
        button = (Button) findViewById(R.id.button);
        button2 = (Button) findViewById(R.id.button2);
        button3 = (Button) findViewById(R.id.button3);

        button.setOnClickListener(new View.OnClickListener(){
            @Override
                    public void onClick(View view){
                textView.setText("Нажата кнопка один");

            }

        });
        button2.setOnClickListener(this);

    }
    public void clickButton3(View view) {
        textView.setText("Нажата кнопка три");
    }

    @Override
    public void onClick(View view) {
        textView.setText("Нажата кнопка два");
    }

}

Код: Выделить всё

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="nightsun.manual.MainActivity"
    android:background="@drawable/mvd">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Large Text"
        android:id="@+id/textView"
        android:layout_alignParentTop="true"
        android:layout_alignParentStart="true" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="1"
        android:id="@+id/button"
        android:layout_below="@+id/textView"
        android:layout_alignParentStart="true" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="2"
        android:id="@+id/button2"
        android:layout_below="@+id/button"
        android:layout_alignParentStart="true" />