java-performance-audit

name	java-performance-audit
description	Expert guidance on auditing a Java Android app's runtime performance with Android Studio Profiler, StrictMode, Layout Inspector, and GPU overdraw. Use this when investigating jank, slow startup, ANRs, or memory leaks.

Java Android Runtime Performance Audit

Instructions

Performance work is measurement-first. Do not optimize without a trace.

1. Establish a Baseline

Measure these before changing any code:

• Startup time — adb shell am start -W ... → TotalTime, WaitTime.
• Frame rate — Profiler → CPU → System Trace, or Macrobenchmark library.
• Memory — Profiler → Memory → record allocations.
• Network — Profiler → Network timeline.

Save traces in docs/perf/ with a date; every future change compares against the baseline.

2. StrictMode — catch main-thread IO immediately

Enable StrictMode in debug builds only:

public class App extends Application {
    @Override
    public void onCreate() {
        super.onCreate();
        if (BuildConfig.DEBUG) {
            StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder()
                    .detectDiskReads()
                    .detectDiskWrites()
                    .detectNetwork()
                    .penaltyLog()
                    .penaltyFlashScreen()
                    .build());
            StrictMode.setVmPolicy(new StrictMode.VmPolicy.Builder()
                    .detectLeakedClosableObjects()
                    .detectLeakedSqlLiteObjects()
                    .detectActivityLeaks()
                    .penaltyLog()
                    .build());
        }
    }
}

Treat every StrictMode log line as a bug to file.

3. Layout Inspector & Hierarchy

• Aim for depth < 8 from the Activity's root. Anything deeper pays for a measure pass per level.
• Flatten nested LinearLayouts into ConstraintLayout (see android-views-xml skill).
• RelativeLayout does two measure passes — prefer ConstraintLayout.
• Remove android:background set to the same color as the parent; it causes overdraw.

Enable Debug GPU Overdraw (developer options) — any red regions on a scrollable list are the main cost to fix.

4. RecyclerView

• Use DiffUtil / ListAdapter; never call notifyDataSetChanged() for content changes.
• Set setHasStableIds(true) + getItemId(position) when IDs are stable.
• Use view pools across RecyclerViews showing the same cell type.
• Set fixed sizes on ImageViews so Glide can downsample (see glide-images skill).
• Binding should do zero allocations on the hot path — move formatters to fields, pre-compute contentDescription.

5. Startup

• Move work out of Application.onCreate — use Jetpack App Startup (androidx.startup) to lazy-initialize libraries.
• Use Baseline Profiles (androidx.benchmark:benchmark-macro-junit4) to generate a profile for R8 to pre-JIT critical paths.
• Defer WorkManager enqueues behind DelayableInitializer.

public class CrashReporterInitializer implements Initializer<Unit> {
    @NonNull
    @Override public Unit create(@NonNull Context context) {
        CrashReporter.init(context);
        return Unit.INSTANCE;
    }
    @NonNull
    @Override public List<Class<? extends Initializer<?>>> dependencies() {
        return List.of();
    }
}

6. Memory

• Profiler → Memory → "Dump Java heap" → filter by Activity. If an Activity instance persists after finish(), you have a leak.
• Use LeakCanary (com.squareup.leakcanary:leakcanary-android) in debugImplementation.
• Common leaks:
  • Inner classes holding implicit outer reference (Fragment listeners, Handlers).
  • Singletons that cache Activity or View.
  • Forgotten BroadcastReceiver / Observer registrations.

7. ANRs

An ANR is any unresponsive main-thread window > 5s. Diagnose with:

• adb bugreport → traces.txt.
• Firebase Crashlytics ANR collection.
• Google Play vitals.

Root causes map 1:1 to what StrictMode catches: disk IO, network, large layouts, broadcast processing on main thread.

8. Background Work

• Use JobScheduler/WorkManager instead of BOOT_COMPLETED receivers.
• Coalesce network calls; prefer OkHttp connection pool reuse (one OkHttpClient per app).
• Batch Room writes in a transaction: db.runInTransaction(() -> { ... }).

9. Profiling Cadence

• Run Systrace on release builds (AOT-compiled) — debug builds with R8 off are not representative.
• Test on a mid-tier device (Pixel 6a, Samsung A-series), not a flagship.
• Record a 30-second trace of the primary user journey each release.

Checklist

• StrictMode is enabled in debug and produces zero violations during the smoke journey.
• Profile GPU Rendering shows no frames above the 16ms line on the main list screen.
• View hierarchy depth is under 8 for every primary screen.
• notifyDataSetChanged() does not appear in production code.
• LeakCanary is integrated in debug and the primary journey produces no leaks.
• Cold startup TotalTime is tracked release-over-release and trending flat or down.
• App Startup library is used; heavy libraries initialize lazily.