Home » Android » java – Error: Gradle: execution failed for task ':app:preDexDebug'

java – Error: Gradle: execution failed for task ':app:preDexDebug'

Posted by: admin May 14, 2020 Leave a comment


I had a self created jar from another projected imported as a library into my other project. When I changed code in that project and exported a new jar to replaced the old one I cannot run my app anymore. I only get the following error:

enter image description here

I have tried removing and adding and adding as dependency, adding as library. Nothing seems to work. I have also done clean build and a rebuild.

How to&Answers:

We’ve seen this problem in the past when our project was compiling with a version of Java different from the one used to compile the library. The magic number is just used to identify class files so that is not the problem here. The issue is the java version (0034.0000 == Java 8).

The easiest thing to do is target Java 6, which may require removing newer syntax from your code. In our case, both the project and library were ours so we were able to add the following to force the version of Java that we needed:

Android Libraries

for android libraries, add this code to the “android” extension object:

android {
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_6
        targetCompatibility JavaVersion.VERSION_1_6

Java Libraries

for java libraries, add this code at the “top level”:

apply plugin: 'java'

version '1.8.1'
group   'com.yourcompany.package'

sourceCompatibility = JavaVersion.VERSION_1_6   //these two lines
targetCompatibility = JavaVersion.VERSION_1_6   //are the only ones that matter

NOTE: the last two lines are the only ones that matter, I added the others just to show where those lines belong, in respect to the rest of your gradle build file.


For us, this was caused by the Android SDK build-tools version. Got the problem on v23.x, but not v22.x. You need to uninstall v23 for cordova to pick v22.

Possibly a symptom rather than a cause, but this may unstick someone in the same situation.


Although your problem seems fixed, I ended up here with a similar error (while building the samples from developer.android.com). In case it’s helpful to others, I was able to solve it by setting JAVA_HOME to the appropriate value. In my case it was:

export JAVA_HOME=/usr/lib/jvm/java-6-openjdk-amd64



sourceCompatibility = JavaVersion.VERSION_X_X
targetCompatibility = JavaVersion.VERSION_X_X

in the Android project gradle file and the Java library gradle file worked for me.

Sorry I would have +1’d it but don’t have a high enough reputation