java.lang.ClassNotFoundException on working app

Something like this happened when I changed the build target to 3.2. After digging around I found that a had named the jar lib folder "lib" instead of "libs". I just renamed it to libs and updated the references on the Java build path and everything was working again. Maybe this will help someone...

I have this problem sometimes with eclipse. What has corrected it for me is to go to Project Properties / Android and change the build target API to a different version and republish. I'll find that corrected it, then I can change it back to the desired build target.

or

You may need to check your proguard.cfg.

Assuming you have linked your libraries properly and that your library projects have the code you need marked for export, the next step you might want to do is to check your proguard settings and make sure you are not stripping out the classes you need.

I was struggling with this quite a bit after I had my app working going directly to the emulator or device from eclipse. The problem I was having was after the app was published (i.e. gone through proguard) and run on the device it was missing classes that were contained in the project. They were being stripped out somehow.

My problem may have been caused when I had tried to use IntelliJ and have switched back to eclipse.

Here is the proguard file that worked for me:

-optimizationpasses 5
-dontusemixedcaseclassnames
-dontskipnonpubliclibraryclasses
-dontpreverify
-verbose
-optimizations !code/simplification/arithmetic,!field/*,!class/merging/*

-keep public class * extends android.app.Activity
-keep public class * extends android.app.Application
-keep public class * extends android.app.Service
-keep public class * extends android.content.BroadcastReceiver
-keep public class * extends android.content.ContentProvider
-keep public class * extends android.app.backup.BackupAgentHelper
-keep public class * extends android.preference.Preference
-keep public class com.android.vending.licensing.ILicensingService

-keepclasseswithmembers class * {
    native <methods>;
}

-keepclasseswithmembers class * {
    public <init>(android.content.Context, android.util.AttributeSet);
}

-keepclasseswithmembers class * {
    public <init>(android.content.Context, android.util.AttributeSet, int);
}

-keepclassmembers enum * {
    public static **[] values();
    public static ** valueOf(java.lang.String);
}

-keep class * implements android.os.Parcelable {
  public static final android.os.Parcelable$Creator *;
}

Check if the package name in the class matches the package name in the manifest file. This worked for me

Setting minifyEnabled to false in my build.gradle file fixed the issue for me.

release {
    minifyEnabled false
}

For me it was just to clean project.

I cleaned project, and run again. And all errors gone.

What helped me in case of Android Studio: The problem occurred after renamning package of large project. So I did almost everything AS offers to clean and refresh the project officially, and it works. I'm not saying this is solution for everyone just in case you're using Android Studio. Done in Android Studio 3.5.1, Windows 10.

• Alex's answer
• Build > Clean Project
• Build > Rebuild Project
• File > Sync with File System
• File > Sync project with Gradle Files
• File > Invalidate Caches / Restart

Make sure that you have package

com.aaraf.demowithdoc //Your Package Name 

com.aaraf.demowithdoc [YOUR PACKAGE NAME] is there in your class where this java.lang.classnotfoundexception is occuring