Static Variables in Java

Static variables in Java are class-level variables that are shared among all instances of the class. Here are the key characteristics:

Key Features

  1. Class-level storage: Belongs to the class rather than any specific instance
  2. Single copy: Only one copy exists regardless of how many objects are created
  3. Shared access: All instances share the same static variable
  4. Memory allocation: Created when the class is loaded and destroyed when the class is unloaded

Declaration Syntax 

class MyClass {
    static int count;  // static variable
    // ...
}

When to Use Static Variables

  • When you need a variable common to all objects of a class
  • For constants (usually combined with final)
  • For maintaining counts or other shared states across instances

Important Notes

  1. Access: Can be accessed using either:

    • Class name: MyClass.count
    • Instance reference: obj.count (not recommended)

  2. Initialization:

    • Default values (0, null, false etc.) if not initialized
    • Can be initialized at declaration or in static blocks

  3. Thread Safety: Static variables are not thread-safe by default - need synchronization in multi-threaded environments

Example 

public class Employee {
    static int employeeCount = 0;  // static variable

    public Employee() {
        employeeCount++;  // increments for each new Employee created
    }

    public static void main(String[] args) {
        new Employee();
        new Employee();
        System.out.println("Total employees: " + Employee.employeeCount);  // Output: 2
    }
}

Static variables are useful for maintaining shared state across all instances of a class, but should be used judiciously to avoid unintended side effects.