What is Android Runtime?

Android Runtime is the system that runs your app code on the device.

👉 Flow:

• You write code → Kotlin/Java
• It becomes bytecode (.dex files)
• Android Runtime converts it → machine code (CPU understands this)

✔ So basically:

Android Runtime = converts and runs your app code on the phone

🔹 Types of Android Runtime

There are mainly two:

1. Dalvik (old)
2. ART (Android Runtime) (modern)

🔹 1. Dalvik (Old Runtime)

Used before Android 5.0.

How it works:

Dalvik uses JIT (Just-In-Time compilation)

👉 Means:

• Code is converted to machine code while the app is running

Flow:

.dex → (runtime conversion) → machine code

Pros:

• Less storage needed
• Faster app installation

Cons:

• App starts slower
• More CPU usage
• Can cause lag (conversion happens during execution)

🔹 2. ART (Android Runtime)

Introduced in Android 5.0, replaces Dalvik.

How it works:

ART uses AOT (Ahead-Of-Time compilation)

👉 Means:

• Code is converted to machine code before the app runs (during install time)

Flow:

.dex → (install time conversion) → machine code

Also uses JIT (modern improvement)

Newer Android versions use:

• AOT + JIT + profiling

Pros:

• Faster app launch 🚀
• Better performance
• Less lag
• Better battery usage

Cons:

• Slightly longer install time
• Uses more storage

🔹 Final Simple Summary

• Dalvik: Converts code while running → slower
• ART: Converts code before running → faster