Keywords in Dart

Keywords are reserved words in the Dart programming language that have a special predefined meaning. These words are part of Dart’s syntax and cannot be used as variable names, function names, or class names.

Understanding keywords is essential because they form the grammar of Dart. Every Dart and Flutter program is built using these keywords.

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Why Keywords Matter

Keywords:

• Define program structure

• Control program flow

• Declare variables, functions, and classes

• Enable object-oriented and asynchronous programming

In Flutter, keywords are constantly used for:

• Widget creation

• State management

• Async API calls

• App navigation and logic

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Categories of Keywords in Dart

For learning purposes, Dart keywords can be grouped into logical categories.

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1. Variable Declaration Keywords

These keywords are used to declare variables.

var

Infers the variable type automatically.

Copyvoid main() {
  var name = 'Rabin';
  print(name);
}

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final

Used when a variable should be assigned only once.

Copyvoid main() {
  final int year = 2025;
  print(year);
}

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const

Used for compile-time constants.

Copyvoid main() {
  const double pi = 3.14159;
  print(pi);
}

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2. Control Flow Keywords

These keywords control the execution flow of a program.

if, else

Copyvoid main() {
  int marks = 60;

  if (marks >= 40) {
    print('Passed');
  } else {
    print('Failed');
  }
}

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switch, case, default

Copyvoid main() {
  int day = 3;

  switch (day) {
    case 1:
      print('Sunday');
      break;
    case 2:
      print('Monday');
      break;
    default:
      print('Other day');
  }
}

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Loop Keywords: for, while, do, break, continue

Copyvoid main() {
  for (int i = 1; i <= 5; i++) {
    if (i == 3) continue;
    print(i);
  }
}

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3. Function-Related Keywords

void

Used when a function does not return a value.

Copyvoid greet() {
  print('Hello Dart');
}

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return

Used to return a value from a function.

Copyint add(int a, int b) {
  return a + b;
}

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4. Object-Oriented Programming Keywords

Dart is an object-oriented language.

class

Copyclass Student {
  String name;
  int age;

  Student(this.name, this.age);
}

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extends

Used for inheritance.

Copyclass Person {
  void speak() {
    print('Speaking');
  }
}

class Student extends Person {}

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this

Refers to the current object.

Copyclass User {
  String name;

  User(this.name);
}

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5. Asynchronous Programming Keywords

These keywords are heavily used in Flutter for API calls and async operations.

async and await

CopyFuture<void> fetchData() async {
  await Future.delayed(Duration(seconds: 2));
  print('Data loaded');
}

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Future

Represents a value that will be available later.

CopyFuture<int> getNumber() async {
  return 10;
}

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6. Null Safety Keywords

null

Represents absence of value.

CopyString? nickname = null;

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late

Used when a variable will be initialized later.

Copylate String token;

void main() {
  token = 'abc123';
  print(token);
}

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Common Beginner Mistakes

• Using keywords as variable names

• Confusing final and const

• Forgetting break in switch cases

• Misusing late and dynamic

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Summary

In this lesson, you learned:

• What keywords are

• Major categories of Dart keywords

• How keywords control program structure and behavior

A strong understanding of keywords will make reading and writing Dart code much easier.

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Assignment

Task 1:
Declare one variable using var, one using final, and one using const. Print all three.

Task 2:
Write a program that checks whether a number is positive, negative, or zero using if and else.

Task 3:
Use a for loop to print numbers from 1 to 10, but skip number 5 using continue.

Task 4:
Create a simple function that returns the square of a number using return.

Task 5 (Thinking):
Explain in your own words when you would use final instead of var in a Flutter app.