OnClickListenerを使う

package com.Btn001;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

public class Btn001 extends Activity implements OnClickListener {
 private TextView message;
 private Button setButton;

 // private Button setButton;
 /** Called when the activity is first created. */
 @Override
 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);

  message = (TextView) this.findViewById(R.id.Message);
  setButton = (Button) this.findViewById(R.id.SetButton);
  setButton.setOnClickListener(this);
 }

 @Override
 public void onClick(View v) {
  /** ボタンを押したときの処理 **/
  if ( v == setButton) {
  message.setText("新しいテキスト");
  }
 }
}