The static Keyword

Belongs to the Class, Not an Object

A static member belongs to the class itself and is shared by every object of that class. You may call it without creating an object.

Static Fields

class Counter {
    static int totalCount = 0;  // shared by all Counter objects
    int instanceCount = 0;      // belongs to each object

    Counter() {
        totalCount++;
        instanceCount++;
    }
}

Counter a = new Counter();
Counter b = new Counter();
System.out.println(Counter.totalCount);  // 2 - shared
System.out.println(a.instanceCount);     // 1 - only this object
System.out.println(b.instanceCount);     // 1

Static Methods

class MathUtils {
    static boolean isEven(int n) { return n % 2 == 0; }
}

boolean result = MathUtils.isEven(8); // no object needed

Static Initialiser Block

Runs once when the class is first loaded:

class Database {
    static String url;
    static {
        url = "jdbc:mysql://localhost/app";
        // load settings, open things once
    }
}

Rules to Remember

• A static method cannot access instance fields directly (no object exists).
• Inside a static method, this is unavailable.
• Static fields are initialised once and shared; be careful with them in multithreading.
• Use static for utility methods that do not depend on object state.

Key Points

• Static members belong to the class and are shared.
• Call them via the class name, not an instance.
• Static code cannot touch instance state.