Static Methods and Variables

11.1.1 What Does Static Mean?

In Java, the static keyword means “this member belongs to the class itself, not to any specific object.”
When you mark a field or method as static:

• You do not need to create an instance to use it.

• The field or method exists once per class, shared by all objects.

Key point:
Non-static members belong to each object, but static members belong to the class.

Where does this matter?

• Static variables are used for data that must be shared across all instances — like a counter that tracks how many objects exist.

• Static methods are used for tasks that don’t depend on any particular object’s state — like utility functions (Math.sqrt()).

11.1.2 Static Fields: One Value Shared by All

A static field is a variable that all instances of a class share.

Example: counting how many objects have been created.

java
public class Counter {
    static int count = 0; // static field

    public Counter() {
        count++; // shared by all instances
    }

    public static void main(String[] args) {
        new Counter();
        new Counter();
        new Counter();
        System.out.println("Number of Counter objects: " + Counter.count);
    }
}

Key point:

• count is declared static.

• Every time you create a Counter object, it increases count.

• The field is shared by all instances — not duplicated.

Without static, each object would have its own separate count, which wouldn’t work here.

11.1.3 Static Methods: No Object Needed

A static method can be called without creating an object.
You can think of it as a class-level tool.

Classic example: main() itself is static:

java
public static void main(String[] args) { ... }

Static methods are useful for:

• Utility tasks (Math.max(), Math.abs()).

• Factory methods that create instances.

• Helper functions that don’t need object data.

Example:

java
public class MathHelper {
    public static int square(int x) {
        return x * x;
    }

    public static void main(String[] args) {
        int result = MathHelper.square(5);
        System.out.println("Square: " + result);
    }
}

Key points:

• You call it like MathHelper.square(5), no object needed.

• Static methods cannot access non-static fields directly — because they don’t belong to any specific object.