{"id":32587,"date":"2024-11-01T09:10:09","date_gmt":"2024-11-01T09:10:09","guid":{"rendered":"http:\/\/atmokpo.com\/w\/?p=32587"},"modified":"2024-11-01T11:54:42","modified_gmt":"2024-11-01T11:54:42","slug":"flutter-course-5-3-size-of-variables-and-instances","status":"publish","type":"post","link":"https:\/\/atmokpo.com\/w\/32587\/","title":{"rendered":"Flutter Course: 5.3 Size of Variables and Instances"},"content":{"rendered":"

<\/p>\n

Flutter is an open-source UI software development kit (SDK) developed by Google that allows you to easily create applications for various platforms such as Android, iOS, and the web. In section 5.3 of this tutorial, we will explore how to declare variables in Flutter and understand the size of instances. Since this topic is fundamental and core to programming, let’s go through it step by step.<\/p>\n

1. What is a variable?<\/h2>\n

A variable is a named space that can store data. In programming, variables are used to manage and manipulate data. There are several ways to declare variables in Flutter, mostly defined using the keywords var<\/code>, final<\/code>, and const<\/code>.<\/p>\n

1.1 var<\/h3>\n

var<\/code> allows the type to be inferred automatically when declaring a variable, creating a variable whose value can be changed. For example:<\/p>\n

void main() {\n    var name = 'Flutter';\n    print(name); \/\/ Output: Flutter\n    name = 'Dart'; \/\/ Can be changed\n    print(name); \/\/ Output: Dart\n}<\/code><\/pre>\n
1.2 final<\/h3>\n
The final<\/code> keyword defines a variable that can be set only once. In other words, it cannot be changed after initialization. This helps enhance the safety of the program.<\/p>\n
void main() {\n    final int age = 10;\n    print(age); \/\/ Output: 10\n    \/\/ age = 20; \/\/ Error: final variables cannot be changed.\n}<\/code><\/pre>\n
1.3 const<\/h3>\n
const<\/code> declares a compile-time constant. This means the value is determined before the program runs and cannot be changed. const<\/code> is mainly used to define constant values or constant lists.<\/p>\n
void main() {\n    const double pi = 3.14;\n    print(pi); \/\/ Output: 3.14\n    \/\/ pi = 3.14159; \/\/ Error: const variables cannot be changed.\n}<\/code><\/pre>\n
2. What is the size of an instance?<\/h2>\n
The size of an instance refers to the amount of memory space an object occupies. This is an important factor in optimizing memory usage efficiency in applications with a lot of dynamic data structures.<\/p>\n
In Flutter, it is very common to create and manage instances of objects. Accordingly, each instance needs to know how much memory its class’s properties and methods occupy.<\/p>\n
2.1 Classes and Instances<\/h3>\n
A class is an essential element of object-oriented programming (OOP) that serves as a template for creating objects. A class can include properties (variables) and methods (functions). An instance is a concrete implementation of such a class.<\/p>\n
class Person {\n    String name;\n    int age;\n\n    Person(this.name, this.age);\n}\n\nvoid main() {\n    var person1 = Person('Alice', 30);\n    var person2 = Person('Bob', 25);\n    print(person1.name); \/\/ Output: Alice\n    print(person2.age); \/\/ Output: 25\n}<\/code><\/pre>\n
2.2 Calculating the Size of an Instance<\/h3>\n
When you want to know the size of an instance in Flutter, you can use memory diagnostic tools or analyze memory usage through development tools to check the size of the instance.<\/p>\n
Generally, the size of an instance depends on the type and number of the class’s properties. Below are examples showing the basic size of objects in memory.<\/p>\n