Test160618.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace _160610
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            button1.Click += button1_Click;
            button2.Click += button2_Click;
            button3.Click += button3_Click;

            //button1.Click += button_Click;
            //button2.Click += button_Click;
            //button3.Click += button_Click;

            //button1.Click += button_Click2;
            //button2.Click += button_Click2;
            //button3.Click += button_Click2;
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        void button1_Click(object sender, EventArgs e)
        {
 	        button1.Text = "ボタン1";
 	        return;
        }

        void button2_Click(object sender, EventArgs e)
        {
            button2.Text = "ボタン2";
 	        return;
        }

        void button3_Click(object sender, EventArgs e)
        {
 	        button3.Text = "ボタン3";
 	        return;
        }        

        void button_Click(object sender, EventArgs e)
        {
            if (sender == null) return;
            if (sender == button1)
                button1.Text = "ボタン1";
            if (sender == button2)
                button2.Text = "ボタン2";
            if (sender == button3)
                button3.Text = "ボタン3";
            return;
        }

        void button_Click2(object sender, EventArgs e)
        {
            if (sender == null || (sender as Button) == null ) return;
            (sender as Button).Text = "ボタン"; 
            return;
        }
    }
}