Statische versus instantiemethoden

public class Main {
  public static void main(String[] args) {
    // Two Person objects hold different names
    Person a = new Person("Ada");
    Person b = new Person("Bob");

    // Instance method: needs an object
    a.greet();
    b.greet();

    // Static method/field: belong to class Utils
    int s = Utils.add(7, 5);               // pure function
    System.out.println("sum = " + s);

    Utils.bumpCounter();
    Utils.bumpCounter();
    System.out.println("counter = " + Utils.counter); // shared across all
  }

  static class Person {
    private String name;
    Person(String name) { this.name = name; }
    void greet() {
      System.out.println("Hello, " + name + "!");
    }
  }

  static class Utils {
    static int counter = 0;                // static field (shared)
    static int add(int x, int y) {         // static method (pure)
      return x + y;
    }
    static void bumpCounter() {            // static method (mutates shared)
      counter = counter + 1;
    }
  }
}