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Mobile Mobile Performance Battery Interview Questions

75 verified Mobile Mobile Performance Battery interview questions — solve with answers, learn from explanations, test yourself in a real simulation.

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Sample questions

Mobile Performance BatteryDifficulty 1
What is a "cold start" of a mobile app?
  • aThe OS creates a brand-new process and initializes everything from scratch✓
  • bThe app resumes exactly where the user left off
  • cThe app receives a push notification while in the foreground
  • dThe app relaunches automatically from a cached UI snapshot after an earlier crash
Explanation:Cold start happens when no process for the app exists in memory. The OS must create the process, start the runtime, build initial objects, and construct the first screen — the slowest launch path.
Mobile Performance BatteryDifficulty 1
What is a "warm start"?
  • aThe very first launch that happens right after the user installs the app
  • bThe app process is still alive in memory, so relaunch skips full initialization✓
  • cThe launch that happens immediately after a device restart
  • dA launch that occurs while the device has no network connection
Explanation:In a warm start, the process wasn't killed — it was just backgrounded. The runtime and many objects already exist, so reaching the UI is faster than a cold start.
Mobile Performance BatteryDifficulty 1
Why is a cold start generally slower than a warm start?
  • aCold start always downloads new UI assets over the network before showing anything
  • bCold start requires the user to re-enter login credentials
  • cCold start rebuilds the process, runtime, and first screen from nothing✓
  • dCold start disables all animations for the session
Explanation:Cold start pays the full cost of process creation, runtime setup, and constructing initial objects and the first screen. Warm start reuses an already-initialized process, so it's much cheaper.
Mobile Performance BatteryDifficulty 1
A user reboots their phone, then hours later taps the app icon for the first time since the reboot. What kind of start does the app perform?
  • aWarm start, because the app was installed before the reboot
  • bA special start type reserved for post-reboot launches only
  • cWarm start, because the OS caches app state across reboots
  • dCold start, because rebooting clears all running processes✓
Explanation:A reboot kills every running process, so there is nothing to resume. The very next launch must create a fresh process — a cold start — regardless of how much time passes afterward.
Mobile Performance BatteryDifficulty 1
Opening the app for the first time in a day feels slow, but switching back to it later without closing it feels instant. What does this pattern point to?
  • aThe slow case is a cold start; the instant case is a warm start✓
  • bThe device's screen refresh rate is misconfigured for this particular app
  • cThe app's network requests are being cached incorrectly
  • dThe difference is caused entirely by battery saver mode
Explanation:The slow first open is a cold start (process was killed after inactivity), while switching back without closing is a warm start (process still alive). Launch-time optimization should target the cold path.
Mobile Performance BatteryDifficulty 1
onAppLaunch():
    loadAllUserData()
    loadAllImages()
    initAnalytics()
    initCrashReporting()
    initAdSdk()
    showFirstScreen()

Every step above runs synchronously before the first screen appears. What's the main concern for cold-start time?
  • ainitAnalytics() must never be called on app launch under any circumstances
  • bNon-essential work delays the first screen and should run after it's shown✓
  • cshowFirstScreen() must be the very first line of the function
  • dloadAllImages() is only valid when called from a background process
Explanation:Everything here blocks the first screen from appearing. Work that isn't needed to render the first screen (ad SDK setup, deep analytics init) should be deferred until after the UI is visible.

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