What is the use of static vs final vs const ? in flutter when to use which ?

Overview

static

final

const

static -- Class-Level (Not Instance)

static

dartCopy
class Counter {
  static int totalCount = 0;   // Shared across ALL instances
  int instanceCount = 0;       // Per-instance

  void increment() {
    totalCount++;       // Class-level
    instanceCount++;    // Instance-level
  }

  static void resetAll() {
    totalCount = 0; // Static method -- only accesses static members
  }
}

final c1 = Counter()..increment()..increment();
final c2 = Counter()..increment();

print(Counter.totalCount); // 3 -- shared across all
print(c1.instanceCount);   // 2 -- c1 only
print(c2.instanceCount);   // 1 -- c2 only

final -- Runtime Constant (Set Once)

final

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class Config {
  final String apiUrl;      // Set in constructor, then fixed
  final DateTime createdAt; // Runtime value -- not known at compile time

  Config(this.apiUrl) : createdAt = DateTime.now();
}

// final local variable
final user = await fetchUser();  // Runtime value, set once
final count = items.length;      // Computed at runtime

const -- Compile-Time Constant

const

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const pi = 3.14159;
const maxRetries = 3;
const appName = 'MyApp';

class AppColors {
  static const primary = Color(0xFF6200EE);     // compile-time
  static const secondary = Color(0xFF03DAC6);
}

// const widget -- Flutter reuses same object (performance!)
const SizedBox(height: 16);
const Text('Hello');

// const list -- deeply immutable
const tags = ['flutter', 'dart']; // Cannot add/remove

Combined Usage in a Class

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class ApiService {
  // static const -- class-level, compile-time, shared
  static const String baseUrl = 'https://api.example.com
  static const int timeout = 30;

  // static -- class-level, mutable
  static int requestCount = 0;

  // final -- instance-level, set once at runtime
  final String authToken;
  final DateTime initializedAt;

  ApiService(this.authToken) : initializedAt = DateTime.now();

  Future<void> get(String endpoint) async {
    requestCount++;  // Shared count across all instances
    // ...
  }
}

// Usage
print(ApiService.baseUrl);      // static const
ApiService.requestCount++;      // static (mutable)
final api = ApiService('token');
print(api.authToken);           // final (instance)

Decision Guide

const

final

static

static const

static final

Quick Comparison

static

final

const

Flutter Rule: Prefer

textCopy

const

for widgets and values. Use

textCopy

final

for runtime values. Use

textCopy

static

for shared class utilities. Combine:

textCopy

static const

for constants shared at class level.