Android Studio编译报错：Multiple dex files define Ljava_cup/runtime/ComplexSymbolFactory

Hey there, let's break down what's causing that dex error in your Weka-Android project and fix your build.gradle setup properly.

The com.android.dex.DexException: Multiple dex files define Ljava_cup/runtime/ComplexSymbolFactory error happens because the same Java class is being included multiple times in your project's dependencies.

Specifically, the Maven dependency nz.ac.waikato.cms.weka:weka-stable:3.8.0 already includes classes from the java-cup library (which contains the ComplexSymbolFactory class). However, somewhere in your dependency tree (either directly or via another library), the same java-cup classes are being pulled in again—either in a different version, or as a duplicate inclusion.

Your previous attempts didn't work because:

• multiDexEnabled true is designed to fix the "method count exceeds 65536" issue, not duplicate class definitions.
• Cleaning and rebuilding only refreshes build caches, it doesn't resolve underlying dependency conflicts.

Instead of falling back to a local Weka 3.6.6 JAR, you can resolve this while keeping the Maven dependency with either of these two approaches:

Option 1: Exclude the Duplicate java-cup Dependency from Weka #

Modify your dependencies block to exclude the java-cup module that's causing the conflict:

implementation ('nz.ac.waikato.cms.weka:weka-stable:3.8.0') {
    // Try this exclusion first (matches Weka 3.8.0's dependency structure)
    exclude group: 'net.sf.squirrel-sql.thirdparty-non-maven', module: 'java-cup'
    // If the above doesn't work, use this more generic rule:
    // exclude group: 'java-cup', module: 'java-cup'
}

This tells Gradle to omit the duplicate java-cup classes from the Weka dependency, ensuring only one copy of the class exists in your build.

Option 2: Force a Single Version of java-cup #

If exclusion doesn't resolve the conflict, you can force all dependencies to use the same version of java-cup. Add this block inside your build.gradle file (outside the android block):

configurations.all {
    // Replace with the exact version used by Weka 3.8.0 (check dependency tree first)
    resolutionStrategy.force 'java-cup:java-cup:0.11a'
}

To find the correct version, run this command in your project's Terminal:

# For macOS/Linux
./gradlew app:dependencies
# For Windows
gradlew app:dependencies

Look through the output to find the version of java-cup that Weka 3.8.0 depends on, then use that version in the force rule.

The older Weka 3.6.6 JAR likely doesn't include the java-cup classes internally, or its dependency chain doesn't pull in a duplicate copy of the library. While this works, using Maven dependencies is better for version management and automatic updates—so fixing the 3.8.0 dependency is the cleaner long-term solution.

内容的提问来源于stack exchange，提问作者Barbarian772