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.toggle method is not working in java in eclipse

so i was following a tutorial on youtube on how to make a minecraft pvp client and when i followed the steps to make a test mod in minecraft that tests the input/to show something in console when you press "b" for example but when i typed in modmanager.testMod.toggle(); eclipse said the method toggle() is undefined for type TestMod.
i changed it to .OnToggle() but it didn't work so i pressed create method "toggle()" and that didn't work either. by the way it created public void toggle() { in TestMod.java

Unity AndroidJavaObject not working without showing errors

I have been trying to call a Java method in unity. Not working for me, even the simplest example from the docs
using System.Collections;
using UnityEngine;
public class ExampleClass : MonoBehaviour {
void Start () {
AndroidJavaObject jo = new AndroidJavaObject ("java.lang.String", "some string");
int hash = jo.Call<int> ("hashCode");
Debug.Log ("hash=" + hash);
}
}
Unity console prints hash=0, which is not the hash code for provided String. Even if I change and use java.lang.StringInvalidClass as class name, unity still reports same result to the console without notifying errors. I can even try to call toString, toStringa, toInvalid2 and they always return empty string without showing errors.
This is a brand new 2d project with only script displayed above, attached to camara object. I am using Ubuntu, Unity 2019.4 and project platform is Android.
Thanks for the assistance.

Answering myself after some time working with unity.
All examples in the web and unity documentation doesn't mention it, which is weird since it is something simple to mention and about confusions: code needs to run as an android application. Editor or even unity remote does not work, in order to use AndroidJavaObject and related classes, your code needs to run as an android application installed in the phone.

How to fix crash handling in android 10

I have a Unity Scene built with Cardboard SDK and exported as a library for Android. The library is used to play videos in cardboard mode on the android app. it's not the whole app, but a part in it. The rest of the android app is built with Kotlin and Java.
I have implemented that and all the functions work as expected, but, exiting the scene crashes the android.
We tried various ways to clear player prefs and even clear memory before closing the scene. But on android it always crashes. I have two android phones with android 9 and 10 for testing.
In the android app, I have made it such that as soon as the app crashes, I try to recover. My crash is that some lateinit var variables are destroyed. Their value becomes null and recovering the previous activity crashes it. So right after I exit the unity scene, I load the dereferenced variables back into memory and everything works again.
Note: I have tried using Application.Quit(); in unity, but it just closes the whole app. On the other hand, I only want to close the running scene
In unity [I call a function goBack in android part to close the app]:
public void GoToHome()
{
Pause();
Stop();
Resources.UnloadUnusedAssets();
PlayerPrefs.DeleteAll();
AndroidJavaClass jc = new AndroidJavaClass("com.unity3d.player.UnityPlayer");
AndroidJavaObject jo = jc.GetStatic<AndroidJavaObject>("currentActivity");
jo.Call("goBack");
}
In App:
public void goBack()
{
UnityPlayer.currentActivity.finish();
finish();
loadDerereferencedVars();
}
This goes perfectly on android 9. On the other phone with android 10, after I close the scene, the app continues to function, but, there comes a message
When I click close app, the app continues to work.
I have checked the logs and there is a null pointer dereference cause for the crash in Unity Main >...
If you'd like to see the Unity Crash Log from LogCat in Android Studio
So, since the app is still running, I thought, it would be better to just hide the crash report and just let the user not know about this crash, but still report it.
I tried enclosing my app in Application and added a method to catch uncaughtException.
here is my application class:
public class MyApp extends Application {
private static final String TAG = "MyAPP";
#Override
public void onCreate() {
super.onCreate();
Thread.setDefaultUncaughtExceptionHandler(
new Thread.UncaughtExceptionHandler() {
#Override
public void uncaughtException (Thread thread, Throwable e) {
handleUncaughtException (thread, e);
}
});
}
/**
* Handles Uncaught Exceptions
*/
private void handleUncaughtException (Thread thread, Throwable e) {
// The following shows what I'd like, though it won't work like this.
Toast.makeText(getApplicationContext(), "Looks like I am having a bad day!", Toast.LENGTH_LONG).show();
Log.e("UncaughtException", "I found an exception!");
// Add some code logic if needed based on your requirement
}
}
Again, this works perfectly in Android 9 and I also got the error reported. However in the phone with android 10, I just get the crash report like the image above and no error is reported.
I want to know why the crash handling is not working and how can I fix it?

I would not finish the Activity you came from, instead just open a new intent (on UnityActivity). When you end this intent the app will come back to the last active Activity.
I will give you my script as an example:
public void sendJobToUnity(String fileName, boolean isNewJob){
//creates a new job. It exists inside the JobSelector Activity
isUnityLoaded = true;
//this is what you are looking for part1
Intent i = new Intent(JobSelector.this, MainUnityActivity.class); //same as (CurrentActivity.this, UnityActivity.this)
//those are how I send some data across the app. just ignore it
//i.putExtra("jobName", fileName);
//i.putExtra("isNewJob",isNewJob);
//i.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
startActivityForResult(i, 1); //this is what you are looking for part2
}
For closing it, in the MainUnityActivity Activity I have an override that Unity sends to Android in order to Unload the activity (not quit it completely cause you cannot load it again if you do it) like this:
#Override
protected void receiveJobAndUnloadUnity(String data){
saveCurrentJob(data); //saves the job it receives from Unity
mUnityPlayer.unload(); //this is what you are looking for part3
}
If you want to unload Unity from android you can put "mUnityPlayer.unload();" wherever you want, provided you have started the Activity the way I've shown you.
Note that "mUnityPlayer" is a default Unity variable and cannot be renamed

Android StartActivityForResult bug

I have an android app which passes some results to the next activity using StartActivityForResult. This is working fine on every phone/tablet I've tested it on except for a Motorola MZ601 which is on Android 4.0.4. By debugging through the code on any other device, it runs the below code:
private void showNextPage() {
Intent i = new Intent(this, InstructionsActivity.class);
startActivityForResult(i, TEST_LEFT_ACTIVITY);
}
This then takes me to the onActivityResult method as expected. Now when I debug through the code on the Motorola instead of taking to the onActivityResult method, it takes me to the onCreate method and reinitialises the results to 0 before moving to the onActivityResult method. So it passes null results over.
Can anyone explain to me why it takes me to the onCreate method before taking my to the onActivityResult method only on this device?
Is it a bug in the version of android or is it the device?

I want to run the application in background of mobile without any GUI in mobile using J2ME?

I am developing the network application in which I want to run my J2ME MIDP application in background without any GUI so that is any way to construct the application is such manner.

try this
set your current Display to null. so there will not be any form or alert running on the screen. But however your code will be running in the background.
Display display = Display.getDisplay(this); // here 'this' points to Midlet
display.setCurrent(null);

it easy just have a code of line on any event for example in the click of button
Display.getDisplay (this).setCurrent (null);
and return back the control via
Display.getDisplay (this).setCurrent (mycanvas);

Yes this code works Good,
display = Display.getDisplay(this);
public void startApp()
{
display.setCurrent(form);
}
public void pauseApp()
{
}
public void hide()
{
Display.getDisplay (this).setCurrent (null);
}
This is will work like, make a button can after clicking it call hide Function, or you call this hide function in constructor so it will hide itself when app start, can you keep unHide statement in appStart() so if you Tab the program then it will unHide app again.
NOTE: you said you are working on Network app, but some mobile will turn off the Internet Connection, when the Mobile screen Turn Off. please check this. and If you found any solution It will be Good to share here.