DalvikDEX

DalvikDEX is a term commonly used in discussions to denote the Dalvik Executable format, the bytecode form used by the Dalvik virtual machine in early Android versions. It typically refers to the .dex files packaged inside Android applications and the tooling that generates and manages them. While not an official separate technology, DalvikDEX appears in documentation as shorthand for the Dalvik-based execution stack, including the process of converting Java class files to Dalvik bytecode and loading these bytecode units at runtime.

Origins and design: Dalvik was introduced to run Android apps on devices with limited resources. The .dex format compresses and optimizes Java bytecode for a register-based execution model, reducing memory usage and improving startup times. A single APK can contain multiple .dex files, and multi-dex support allows apps to exceed the traditional method-count limit associated with early Android releases.

Structure and mechanics: A .dex file comprises a header, and sections for string identifiers, type identifiers, prototype identifiers, field identifiers, method identifiers, and class definitions, followed by data blocks containing the bytecode for methods. Dalvik's instructions use a register-based encoding and compact operand representation. Tools such as the dx utility convert Java class files into DEX format, and runtime environments load, verify, and execute these DEX units.

Tools, runtime, and evolution: The Android toolchain has evolved to include d8 as a modern replacement for dx in building DEX files. Historically, the Dalvik VM executed DEX bytecode, with the runtime performing just-in-time compilation or interpretation. In Android 5.0 Lollipop and later, ART largely supplanted Dalvik as the default runtime, though DEX remains the common input format for Android apps.

See also: Dalvik, DEX format, ART, Android.