What is the static Keyword in Java?

The static keyword indicates that a member belongs to the class itself rather than to instances of the class.

1. Static Variables (Class Variables)

Shared across all objects of the class. Only one copy exists in memory.

class Counter {
    static int count = 0; // Static variable - shared
    
    Counter() {
        count++;
        System.out.println("Object created. Total objects: " + count);
    }
    
    public static void main(String[] args) {
        Counter c1 = new Counter(); // count = 1
        Counter c2 = new Counter(); // count = 2
        Counter c3 = new Counter(); // count = 3
    }
}

2. Static Methods

Can be called without creating an object. They can only access static members directly.

class MathUtils {
    public static int square(int x) {
        return x * x;
    }
    
    public static int add(int a, int b) {
        return a + b;
    }
}

public class Test {
    public static void main(String[] args) {
        // Calling static methods without object
        System.out.println(MathUtils.square(5)); // 25
        System.out.println(MathUtils.add(10, 20)); // 30
    }
}

3. Static Block

Executed once when the class is first loaded into memory (before main).

class Database {
    static String connectionUrl;
    static String username;
    
    // Static block for initialization
    static {
        System.out.println("Static block executed");
        connectionUrl = "jdbc:mysql://localhost:3306/mydb";
        username = "admin";
    }
    
    static void connect() {
        System.out.println("Connecting to: " + connectionUrl);
    }
    
    public static void main(String[] args) {
        System.out.println("Main method started");
        Database.connect();
    }
}
// Output:
// Static block executed
// Main method started
// Connecting to: jdbc:mysql://localhost:3306/mydb

Rules for static

• Static methods cannot access non-static members directly
• Cannot use this or super in static context
• Static nested classes can have static members

Employee ID Generator Example

class Employee {
    private static int nextId = 1000;
    private int empId;
    private String name;
    
    Employee(String name) {
        this.name = name;
        this.empId = nextId++;
    }
    
    void display() {
        System.out.println("ID: " + empId + ", Name: " + name);
    }
    
    static void showNextId() {
        System.out.println("Next ID will be: " + nextId);
    }
    
    public static void main(String[] args) {
        Employee e1 = new Employee("Alice");
        Employee e2 = new Employee("Bob");
        e1.display(); // ID: 1000, Name: Alice
        e2.display(); // ID: 1001, Name: Bob
        Employee.showNextId(); // Next ID will be: 1002
    }
}

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