روز 16: متغیرهای جاوا: مستندات جامع

Data Type   Default Value   Size (bits) Range/Example
byte    0   8   -128 to 127
short   0   16  -32,768 to 32,767
int 0   32  -2³¹ to 2³¹-1
long    0L  64  -2⁶³ to 2⁶³-1
float   0.0f    32  3.4e-038 to 3.4e+038
double  0.0d    64  1.7e-308 to 1.7e+308
char    '\u0000'    16  'A', '1', '$'
boolean false   1 (JVM-dependent)   true or false

Data Type   Default Value   Example
String  null    "Hello"
Arrays  null    int[] arr = {1, 2, 3};
Classes null    Tourist tourist = new Tourist();

Declared inside methods/constructors/blocks.
No default value (must be initialized before use).
Lifetime: Exists only while the method executes.

public void calculate() {
    int localVar = 10; // Local variable (must be initialized)
    System.out.println(localVar);
}

Declared inside a class, outside methods.
Have default values (if not initialized).

Two types:
    Static (static keyword) → Class-level (shared).
    Non-Static (no keyword) → Instance-level (object-specific).

public class Tourist {
    static int globalStaticVar = 1000; // Static (class-level)
    int globalNonStaticVar = 500;      // Non-static (instance-level)
}

Variable Type   Default Value
Global (Static/Non-Static)  Yes (e.g., 0, null)
Local   No (Compiler Error if Uninitialized)

If a local variable has the same name as a global variable, the local variable takes precedence.

public class Tourist {
    static int amount = 100000; // Global static

    public void havingDinner() {
        int amount = 2000; // Local variable (shadows global)
        System.out.println(amount); // Prints 2000 (local)
    }

    public static void main(String[] args) {
        System.out.println(Tourist.amount); // 100000 (global)
        Tourist t = new Tourist();
        t.havingDinner(); // 2000 (local)
    }
}

public class Example {
    int value = 100; // Non-static global

    public void printValue() {
        int value = 50; // Local variable
        System.out.println(value); // 50 (local)
        System.out.println(this.value); // 100 (global)
    }
}

Summary Table
Feature Local Variables Global Variables
Scope   Inside method/block Class-level
Default Value   ❌ No (must initialize)    ✔ Yes
Lifetime    Method execution    Entire program (static) / Object lifetime (non-static)
Shadowing   Can override global Can be accessed via ClassName.staticVar or this.nonStaticVar