我的字符串没有出现在我的数据库中

private Table income;
private Table expense;
String title,comment;
int amount;

EditText add;
Button add_btn;
/** Called when the activity is first created. */
@Override
 public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    DatabaseHelper helper = new DatabaseHelper(this);
    SQLiteDatabase db = helper.getWritableDatabase();
    expense = new Table(db,helper.TABLE_1);
    income = new Table(db,helper.TABLE_2);
    add_btn = (Button)findViewById(R.id.add_btn);
    add = (EditText)findViewById(R.id.add);
    add_btn.setOnClickListener(this);
}

@Override
public void onClick(View v) {
    title = add.getText().toString();
    income.insertTable(title, 100, " test");
    expense.insertTable("another title", 50, "blah blah");
}

}