android 开发 跨activity调取数据 总是报空指针异常的错误

public class dataActivity extends Activity {

private ListView listView;
private String[] adapterData;

String rename = getIntent().getStringExtra("rename");
String repasswd = getIntent().getStringExtra("repasswd");
SQLiteDatabase db;

public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.dataactivity);
db = SQLiteDatabase.openOrCreateDatabase(dataActivity.this
.getFilesDir().toString() + "/test.dbs", null);
Cursor uatr = db.rawQuery(
"select ua from tb_user1 where name=? and password=?",
new String[] { rename, repasswd });
Cursor uitr = db.rawQuery(
"select ui from tb_user1 where name=? and password=?",
new String[] { rename, repasswd });
Cursor jitr = db.rawQuery(
"select ji from tb_user1 where name=? and password=?",
new String[] { rename, repasswd });

listView = (ListView) findViewById(R.id.showdata);

adapterData = new String[] { uatr.toString(), uitr.toString(),
jitr.toString() };

ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(
dataActivity.this, android.R.layout.simple_list_item_1,
adapterData);

listView.setAdapter(arrayAdapter);
}
}