Non-static 'sleep(long)' cannot be referenced from a static context

Question

I am trying to call function sleep from my Utils as the below code:

@Override
                        public void onError(String err) {
                            log("A pinger died");
                            if (errorHandlingMode.equals(SpeedtestConfig.ONERROR_FAIL)) {
                                PingStream.this.onError(err);
                                return;
                            }
                            if (errorHandlingMode.equals(SpeedtestConfig.ONERROR_ATTEMPT_RESTART) || errorHandlingMode.equals(SpeedtestConfig.ONERROR_MUST_RESTART)) {
                                Utils.sleep(100);
                                init();
                            }
                        }

and this is the full function I have:

private void init() {
        if (stopASAP) return;
        if (c != null) {
            try {
                c.close();
            } catch (Throwable ignored) {
            }
        }
        new Thread() {
            public void run() {
                if (pinger != null) pinger.stopASAP();
                if (remainingPings <= 0) return;
                try {
                    c = new Connection(server, connectTimeout, soTimeout, recvBuffer, sendBuffer);
                    if (stopASAP) {
                        try {
                            c.close();
                        } catch (Throwable ignored) {
                        }
                        return;
                    }
                    pinger = new Pinger(c, path) {
                        @Override
                        public boolean onPong(long ns) {
                            boolean r = PingStream.this.onPong(ns);
                            if (--remainingPings <= 0 || !r) {
                                onDone();
                                return false;
                            } else return true;
                        }

                        @Override
                        public void onError(String err) {
                            log("A pinger died");
                            if (errorHandlingMode.equals(SpeedtestConfig.ONERROR_FAIL)) {
                                PingStream.this.onError(err);
                                return;
                            }
                            if (errorHandlingMode.equals(SpeedtestConfig.ONERROR_ATTEMPT_RESTART) || errorHandlingMode.equals(SpeedtestConfig.ONERROR_MUST_RESTART)) {
                                Utils.sleep(100);
                                init();
                            }
                        }
                    };
                } catch (Throwable t) {
                    log("A pinger failed hard");
                    try {
                        c.close();
                    } catch (Throwable ignored) {
                    }
                    if (errorHandlingMode.equals(SpeedtestConfig.ONERROR_MUST_RESTART)) {
                        Utils.sleep(100);
                        init();
                    } else onError(t.toString());
                }
            }
        }.start();
    }

I found a compile time error with Non-static 'sleep(long)' cannot be referenced from a static context

and this is the below Utils I have:

package com.live.flutter_telephony_rf_example.core.base

import java.net.URLEncoder

object Utils {
    fun urlEncode(s: String?): String? {
        return try {
            URLEncoder.encode(s, "utf-8")
        } catch (t: Throwable) {
            null
        }
    }

    fun sleep(ms: Long) {
        try {
            Thread.sleep(ms)
        } catch (t: Throwable) {
        }
    }

    fun sleep(ms: Long, ns: Int) {
        try {
            Thread.sleep(ms, ns)
        } catch (t: Throwable) {
        }
    }

    fun url_sep(url: String): String {
        return if (url.contains("?")) "&" else "?"
    }
}

Screen shot error:

@Zoe I don't think so, but let me check this, thanks for your suggestion — Mahmoud Al-Haroon, Apr 13 '21 at 12:28
I don't think it does actually @Zoe. This question is about Kotlin/Java interop. — Henry Twist, Apr 13 '21 at 12:28
The solution here would be to use `Utils.INSTANCE.sleep(...)`. In Kotlin, companion objects are singletons, as opposed to their methods being static. Therefore in Java you have to do the extra step of retrieving the singleton instance and then calling the method. — Henry Twist, Apr 13 '21 at 12:29
@HenryTwist yes exactly that what I am talking about, I think he didn't read carefully — Mahmoud Al-Haroon, Apr 13 '21 at 12:29
@Dude because I working on a flutter project as I am creating a flutter plugin but mainly it's android part, I think it is my mistake :) — Mahmoud Al-Haroon, Apr 13 '21 at 12:32
Ah, I shouldn't have answered @Zoe sorry. I'll vote it as a duplicate. — Henry Twist, Apr 13 '21 at 12:34

score 1 · Accepted Answer · answered Apr 13 '21 at 12:34

The problem here is that Kotlin doesn't have static methods at all. So calling Utils.sleep(...) isn't a valid approach.

Instead Kotlin has objects, which are treated and instantiated as singletons. Therefore when calling from Java you need the extra step of retrieving the singleton instance which Kotlin exposes as INSTANCE. So something like this:

Utils.INSTANCE.sleep(...);

As an alternative solution, you could also use the @JvmStatic annotation which will allow the method to be interpreted as static:

@JvmStatic
fun sleep(...)

Non-static 'sleep(long)' cannot be referenced from a static context

1 Answers1