The static Keyword in Java

The static keyword in Java means "this belongs to the class, not to any one object". A static variable is shared by every object, and a static method can be called without creating an object at all. Once you see the difference between class-level and object-level, a lot of Java suddenly makes sense.

What does static mean in Java?

Think of a classroom. Each student has their own notebook (instance variables), but there's only one whiteboard at the front that everyone shares. If the teacher writes on it, every student sees the same thing. Static members are the whiteboard.

public class Ticket {
    static int created = 0;   // ONE copy, shared by all tickets (the whiteboard)
    final int number;         // each ticket has its OWN number (a notebook)

    Ticket() {
        created++;
        number = created;
    }
}

Ticket a = new Ticket();
Ticket b = new Ticket();
Ticket c = new Ticket();

System.out.println(a.number + ", " + b.number + ", " + c.number);
System.out.println("Tickets created: " + Ticket.created);

1, 2, 3
Tickets created: 3

• static int created — exists once, on the class. All three constructors incremented the same counter.
• final int number — every ticket gets its own copy with its own value.
• Ticket.created — static members are accessed through the class name, not an object.

What can be static in Java?

static int created = 0;   // shared counter

static double toFahrenheit(double c) {
    return c * 9 / 5 + 32;
}
// Temperature.toFahrenheit(25)

public static final double VAT_RATE = 0.18;

static final Map<String, Integer> CODES = new HashMap<>();
static {
    CODES.put("LK", 94);
    CODES.put("US", 1);
}

class Pizza {
    static class Builder { /* ... */ }
}
// new Pizza.Builder()

import static java.lang.Math.max;
// max(3, 7) instead of Math.max(3, 7)

Static methods: no object required

If a method doesn't need any object's data, make it static. You've used plenty already: Math.max(3, 7), Integer.parseInt("42"), List.of(1, 2, 3).

public class Temperature {
    static double toFahrenheit(double celsius) {
        return celsius * 9 / 5 + 32;
    }
}

System.out.println(Temperature.toFahrenheit(25));   // no 'new Temperature()' needed

77.0

Why is main static?

When your program starts, no objects exist yet. A static main lets the JVM call YourClass.main(args) straight away, without needing to create a YourClass object first. That's also why beginners hit this error:

public class App {
    void greet() { System.out.println("Hello"); }

    public static void main(String[] args) {
        greet();              // ✘ non-static method greet() cannot be referenced from a static context
        new App().greet();    // ✔ create an object, then call its method
    }
}

Static blocks: one-time setup

A static block runs once, the first time the class is used, before any static method or object creation:

import java.util.HashMap;
import java.util.Map;

public class DialCodes {
    static final Map<String, Integer> CODES = new HashMap<>();

    static {
        System.out.println("Loading dial codes...");
        CODES.put("LK", 94);
        CODES.put("US", 1);
        CODES.put("GB", 44);
    }

    static int codeFor(String country) {
        return CODES.getOrDefault(country, -1);
    }
}

System.out.println(DialCodes.codeFor("LK"));
System.out.println(DialCodes.codeFor("GB"));

Loading dial codes...
94
44

Notice "Loading…" printed only once, even though we called codeFor twice.

When should you avoid static?

• Don't make ordinary data static just to avoid creating objects. A static balance would mean every account shares one balance!
• Mutable static state is shared by all threads, which can cause bugs in multi-threaded code. See thread-safe lists.
• Static methods can't be overridden, only hidden, so they don't take part in polymorphism.

Quick recap

What's next?

static is often paired with final to make constants. Learn what final does next, or browse the full Java keywords list.