After adding library show this error Didn't find class ".MainActivity" on path: DexPathList

Question

build.gradle

apply plugin: 'com.android.application'

android {

compileSdkVersion 27
defaultConfig {
    applicationId "com.appium_new"
    minSdkVersion 26
    targetSdkVersion 27
    versionCode 1
    versionName "1.0"
    testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

    packagingOptions {
        exclude 'lang-708-input.txt'
        exclude 'java.policy'
    }

}
buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
    }
}

}

dependencies {

implementation fileTree(include: ['*.jar'], dir: 'libs')
implementation 'com.android.support:appcompat-v7:27.1.1'
implementation 'com.android.support.constraint:constraint-layout:1.1.3'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.2'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
implementation files('src/libs/byte-buddy-1.8.15.jar')
implementation files('src/libs/commons-exec-1.3.jar')
implementation files('src/libs/commons-lang3-3.9.jar')
implementation files('src/libs/commons-lang3-3.9-sources.jar')
implementation files('src/libs/commons-lang3-3.9-test-sources.jar')
implementation files('src/libs/commons-lang3-3.9-tests.jar')
implementation files('src/libs/guava-25.0-jre.jar')
implementation files('src/libs/java-client-7.3.0.jar')
implementation files('src/libs/okhttp-3.11.0.jar')
implementation files('src/libs/okio-1.14.0.jar')
implementation files('src/libs/selenium-server-standalone-3.141.59.jar')

}

After adding the last library i.e. implementation files('src/libs/selenium-server-standalone-3.141.59.jar') its show below error, if I remove this library then it work fine

2019-11-13 18:05:44.994 12737-12744/? E/com.appium_new: Failed to send DDMS packet REAQ to debugger (-1 of 20): Broken pipe

2019-11-13 18:05:45.587 12737-12737/? E/AndroidRuntime: FATAL EXCEPTION: main Process: com.appium_new, PID: 12737

java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.appium_new/com.appium_new.MainActivity}: java.lang.ClassNotFoundException: Didn't find class "com.appium_new.MainActivity" on path: DexPathList[[zip file "/system/framework/org.apache.http.legacy.boot.jar", zip file "/data/app/com.appium_new-0MtEr8TXu2cbQ_krT1jqPg==/base.apk"],nativeLibraryDirectories=[/data/app/com.appium_new-0MtEr8TXu2cbQ_krT1jqPg==/lib/x86, /system/lib]]
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2843)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6669)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
 Caused by: java.lang.ClassNotFoundException: Didn't find class "com.appium_new.MainActivity" on path: DexPathList[[zip file "/system/framework/org.apache.http.legacy.boot.jar", zip file "/data/app/com.appium_new-0MtEr8TXu2cbQ_krT1jqPg==/base.apk"],nativeLibraryDirectories=[/data/app/com.appium_new-0MtEr8TXu2cbQ_krT1jqPg==/lib/x86, /system/lib]]
    at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:134)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
    at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:69)
    at android.app.Instrumentation.newActivity(Instrumentation.java:1215)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2831)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) 
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) 
    at android.os.Handler.dispatchMessage(Handler.java:106) 
    at android.os.Looper.loop(Looper.java:193) 
    at android.app.ActivityThread.main(ActivityThread.java:6669) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) 
    Suppressed: java.lang.NoClassDefFoundError: Failed resolution of: Landroid/support/v7/app/AppCompatActivity;
    at java.lang.VMClassLoader.findLoadedClass(Native Method)
    at java.lang.ClassLoader.findLoadedClass(ClassLoader.java:738)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:363)
            ... 15 more
 Caused by: java.lang.ClassNotFoundException: Didn't find class "android.support.v7.app.AppCompatActivity" on path: DexPathList[[zip file "/system/framework/org.apache.http.legacy.boot.jar", zip file "/data/app/com.appium_new-0MtEr8TXu2cbQ_krT1jqPg==/base.apk"],nativeLibraryDirectories=[/data/app/com.appium_new-0MtEr8TXu2cbQ_krT1jqPg==/lib/x86, /system/lib]]
    at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:134)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
            ... 18 more

Answer 1

After adding library gradle haven't synced properly so it's showing the error, "Didn't find class '.MainActivity' ":

The main problem is some gradle files have same internal files like:-

implementation files('src/libs/okhttp-3.11.0.jar') implementation files('src/libs/okio-1.14.0.jar') or

implementation files('src/libs/commons-lang3-3.9.jar') implementation files('src/libs/commons-lang3-3.9-sources.jar') implementation files('src/libs/commons-lang3-3.9-tests.jar')

so it's not syncing successfully ,

Or second option is to use gradle versions like

implementation("com.squareup.okhttp3:okhttp:4.2.2")
 implementation 'com.github.apache:commons-lang:LANG_3_8_1_RC1'

and put version according to your need...

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The main problem is ClassNotFoundException so check on this link there have given many solution. use it and see what work with your project.