public void button1_onClick(View view){
String SDFile = android.os.Environment.getExternalStorageDirectory().getPath()
+ "/iPentec.SDCardFileAccess/memo.txt";
File file = new File(SDFile);
file.delete();
Toast t = Toast.makeText(this, "ファイルを削除しました", Toast.LENGTH_LONG);
t.show();
}