和 php 类似, 使用 Static 可以标记类的变量和方法

Person.java

public class Person {
    String name;
    int age;
    static String gender = "male";

    // 还可以声明静态代码块
    static {
      gender = "female";
    }

    Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    static void sayHello() {
        System.out.println("hello");
        System.out.println(gender);
    }
}

Main.java

class Main {
    public static void main(String[] args) {
        String gender = Person.gender;
        Person.sayHello();
    }
}