DEX Method-Count Bin Packer: Multidex SDK Integration

Third-party SDKs to integrate

Build settings

R8 / ProGuard shrink 0%

Multidex enabled

Build result

✓ Builds fine

Total methods

DEX files

Last DEX fill

Est. cold-start hit

0 ms

How it works

Every Android APK compiles Java/Kotlin bytecode into one or more .dex files, and a single DEX file can reference at most 65,536 methods (the classic "64K method limit" — the reference index is a 16-bit field). Add enough third-party SDKs and your app blows past it, so the build tool splits classes across multiple DEX files (multidex).

capacity per DEX = 65,536 methods
item size(sdk)   = methods(sdk) × (1 − shrink)
bin packing:      place each item in the first DEX
                   with room; if none fits, open a new DEX

This is a textbook bin-packing problem (NP-hard in general). Two placement orders are compared here:

Naive order — SDKs are packed in the order you enabled them, First-Fit only.
First-Fit Decreasing (FFD) — SDKs are sorted largest-methods-first, then First-Fit. FFD is a well-known ≤ 11/9·OPT + 1 approximation and in practice needs the same or fewer DEX files than naive ordering.

R8/ProGuard shrink removes unused classes/methods from each SDK (tree-shaking), directly reducing its item size before packing. Multidex off means only one DEX is allowed — if the total exceeds 65,536 methods the build fails outright, which is why real Android projects with several SDKs almost always need multiDexEnabled true.

The cold-start estimate is an order-of-magnitude illustration of a real, well-documented effect: ART must verify every method's bytecode at install/first-run time, and opening each additional DEX file costs a fixed lookup/IO overhead — roughly totalMethods × 0.0008 ms + (dexFiles − 1) × 12 ms here. More SDKs and more DEX splits measurably slow app startup, which is why teams audit "is this SDK worth its method count" before adding one.

65,536 methods / DEX file

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