Static members (static fields, static methods, static blocks)

static members belong to the class itself, not to individual instances. They are shared among all objects of the class.

Static fields

One copy shared by all instances.

class Counter {
    static int count = 0;
    Counter() {
        count++;
    }
}
Counter c1 = new Counter(); // count = 1
Counter c2 = new Counter(); // count = 2
System.out.println(Counter.count); // Access via class name

Static methods

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

class MathUtils {
    static int add(int a, int b) {
        return a + b;
    }
}
int sum = MathUtils.add(5, 3);

Static blocks

Executed when the class is first loaded. Used for static initialization.

class Database {
    static String url;
    static {
        url = "jdbc:mysql://localhost:3306/db";
        System.out.println("Static block executed");
    }
}

Order of execution: Static blocks run in the order they appear, before any constructor or static method calls.

Common uses:

• Constants: public static final double PI = 3.14159;
• Factory methods: public static Car createDefault() { ... }
• Utility classes (e.g., Math, Collections)