Multi-Release JAR Manifest Attribute: Essential Condition for Version Selection
A team has a multi-release JAR that supports both Java 11 and Java 17. They want to ensure that when running on Java 17, the version-specific classes in META-INF/versions/17 are used. Which condition must be true?
Quick Answer
The answer is that the manifest must contain 'Multi-Release: true'. This is the essential condition because the Java runtime explicitly checks for this manifest attribute to enable version selection from the `META-INF/versions/` directory; without it, the JVM ignores all versioned directories and falls back to the root classes, even if the JAR was compiled with `--multi-release 17`. On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this concept tests your understanding of the multi-release JAR manifest requirement as a gatekeeper for modular versioning—a common trap is assuming that merely placing classes in versioned folders is enough, when in fact the runtime only reads them if the manifest flag is present. A reliable memory tip is to think of the manifest as a "key" that unlocks the versioned directories: no `Multi-Release: true`, no version-specific class loading.
⚠ Common exam trap
Oracle often tests the misconception that the `--multi-release` compiler or jar tool option alone enables version selection at runtime, when in fact the manifest entry `Multi-Release: true` is the sole runtime trigger.
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 manifest must contain 'Multi-Release: true'
The Java runtime checks for the `Multi-Release: true` entry in the JAR's manifest file to enable multi-release JAR functionality. Without this manifest attribute, the JVM ignores versioned directories under `META-INF/versions/` and uses only the root classes, even if the JAR was compiled with `--multi-release 17`.
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 must have a module-info.class in the root
Why it's wrong here
A module-info.class is not required for multi-release JARs.
- ✗
The JAR must be placed on the module path
Why it's wrong here
The JAR can be on classpath or module path; the manifest is key.
- ✗
The JAR must be created using the --multi-release 17 option
Why it's wrong here
The --multi-release option adds versioned directories but the manifest entry is still needed at runtime.
- ✓
The manifest must contain 'Multi-Release: true'
Why this is correct
The manifest entry is required to activate multi-release behavior.
Go deeper
Related to this question
About these practice questions
This 1Z0-829 question is part of Courseiva's 513-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
Same concept, more angles
2 more ways this is tested on 1Z0-829
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which TWO are characteristics of a multi-release JAR (MR-JAR)?
easy- ✓ A.The root of the JAR contains classes for the oldest supported version.
- B.The version directory must be named with the full version string like "9.0.4".
- ✓ C.It uses the META-INF/versions/ directory structure.
- D.It can only contain a single version of each class.
- E.It is created using the jlink tool.
Why A: In a multi-release JAR (MR-JAR), the root of the JAR contains the classes compiled for the oldest supported Java version. This ensures backward compatibility: when the JAR is run on an older JVM that does not understand the META-INF/versions directory, it will use the classes from the root. The JVM automatically selects the appropriate versioned class from the META-INF/versions/<version>/ directory based on the major version of the running Java runtime.
Variation 2. A company uses a multi-release JAR (MR-JAR) that contains classes for Java 9 and Java 11 in `META-INF/versions/9/` and `META-INF/versions/11/` respectively. The application runs on Java 17. Which version of a class that exists in both versioned directories is loaded?
hard- A.The version from META-INF/versions/9/
- B.The version from the root of the JAR
- ✓ C.The version from META-INF/versions/11/
- D.The version from META-INF/versions/17/
Why C: In a multi-release JAR (MR-JAR), the Java runtime selects the versioned directory that matches the major version of the running Java platform, or the highest versioned directory that does not exceed that version. Since the application runs on Java 17, and the highest available versioned directory is for Java 11 (META-INF/versions/11/), the class from that directory is loaded. The root directory is used only when no appropriate versioned directory exists.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 1Z0-829 practice question is part of Courseiva's free Oracle certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 1Z0-829 exam.