Question 423 of 513
1Z0-829 Java Platform Overview and Packaging Practice Question
A developer has written a Java class that uses external libraries packaged as JAR files. The application runs correctly when launched from an IDE but fails with a ClassNotFoundException when run from the command line using `java -cp`. What is the most likely cause?
⚠ Common exam trap
It's easy for candidates to confuse the classpath with the module path, or assume that `java -jar` automatically resolves all dependencies, when in fact it only reads the `Class-Path` manifest entry and does not combine with `-cp` unless explicitly set.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The JAR files are not listed in the classpath argument.
When running a Java application from the command line with `java -cp`, the classpath must explicitly include all JAR files and directories containing the required classes. If the external library JARs are not listed in the `-cp` argument, the class loader cannot find them, resulting in a `ClassNotFoundException`. IDEs typically manage the classpath automatically, which is why the application works there but fails from the command line.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The JAR files are not listed in the classpath argument.
Why this is correct
The classpath must explicitly list all required JAR files.
- ✗
The classpath is missing the directory containing the class files.
Why it's wrong here
The class files directory is usually included, but the issue is missing JARs.
- ✗
The JAR files are not in the module path.
Why it's wrong here
Module path is for modular JARs; non-modular JARs go on classpath.
- ✗
The Java command should use java -jar instead.
Why it's wrong here
java -jar is only for executable JARs with a manifest; doesn't fix ClassNotFoundException.
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Last reviewed: Jun 25, 2026
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