Difficulty: Medium
Correct Answer: Because Android uses its own virtual machine and DEX bytecode format instead of standard JVM bytecode, so code must be converted first.
Explanation:
Introduction / Context:
Android applications are commonly written in Java or Kotlin, which leads many developers to assume that standard Java Virtual Machine bytecode can run directly on Android. This question tests knowledge of the real execution environment, including the role of Dalvik or ART and the special DEX bytecode format, which differs from standard JVM class files.
Given Data / Assumptions:
Concept / Approach:
Android originally used the Dalvik virtual machine and now uses the Android Runtime (ART). Both are designed for mobile environments and use a special bytecode format called DEX (Dalvik Executable). During the build process, normal Java class files are converted into one or more .dex files. These DEX files are then interpreted or ahead of time compiled by the Android Runtime. Because of this architectural choice, the system cannot execute raw JVM bytecode directly.
Step-by-Step Solution:
Step 1: Understand that the standard Java platform uses the JVM with .class files and possibly .jar archives.Step 2: Recognize that Android tooling runs an additional step, converting compiled .class files into the DEX format that the Android Runtime understands.Step 3: Note that the Android Runtime is optimized for mobile constraints and does not implement the full JVM specification.Step 4: Therefore, a file containing ordinary JVM bytecode cannot simply be dropped onto an Android device and executed; it must be transformed into DEX first.Step 5: This reasoning matches option A, which explains the use of a different virtual machine and bytecode format.
Verification / Alternative check:
Official Android build tools such as d8 and R8 are dedicated to converting JVM bytecode into DEX. The presence of these tools and the structure of .apk or .aab packages, which contain classes.dex files, confirm that Android expects DEX bytecode, not raw .class files. This evidence strongly supports the explanation given in option A.
Why Other Options Are Wrong:
Option B is wrong because Android clearly uses a runtime environment, originally Dalvik and later ART, to manage application execution. Option C is misleading; while memory usage is a consideration, it is not the fundamental reason for rejecting JVM bytecode. Option D is incorrect because Android does not run only native C plus plus code; it is primarily a managed runtime environment that executes DEX bytecode and may include native libraries in some applications.
Common Pitfalls:
Developers sometimes attempt to run unmodified desktop Java libraries on Android, unaware of DEX and runtime differences, leading to compatibility problems. Another common mistake is misunderstanding how multidex works when applications have many methods. Appreciating the role of DEX and the Android Runtime helps developers structure their projects, manage dependencies, and troubleshoot class loading issues more effectively.
Final Answer:
Because Android uses its own virtual machine and DEX bytecode format instead of standard JVM bytecode, so code must be converted first.
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