idea测试okhttp时构建出错

没用过okhttp，想测试一下。

public class t {
    OkHttpClient client = new OkHttpClient();

    String run(String url) throws IOException {
        Request request = new Request.Builder()
                .url(url)
                .build();

        try (Response response = client.newCall(request).execute()) {
            return response.body().string();
        }
    }
}

结果报这样的错，不知道怎么解决。