public class ButtonClickListener implements OnClickListener{

    private Context context;

    ButtonClickListener(Context c){
        context = c;
    }

    public void onClick(View v) {
        Toast.makeText(
                context.getApplicationContext(),
                "ボタンが押されました",
                Toast.LENGTH_LONG).show();
    }

}

public class AndroidsCastleActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        Button btn = (Button)findViewById(R.id.sampleButton);
        btn.setOnClickListener( new ButtonClickListener(this) );
    }
}