理论

概念

static是静态修饰符，静态指只要程序在运行，那么这块内存就会一直存在。

案例

成员变量

public class Person {
    //将count设为静态变量，每次运行会优先执行且只执行一次
    private static int count = 0;
    int id;
    String name;
    int age;
    //将Id与count同步
    public Person() {
        id = ++count;
    }
    public String toString() {
        return "Id:" + id + ", Name:" + name + ", Age:" + age;
    }
    //主方法
    public static void main(String[] args) {
        Person p1 = new Person();
        p1.name = "张三";
        p1.age = 10;
        Person p2 = new Person();
        p2.name = "李四";
        p2.age = 12;
        System.out.println(p1);
        System.out.println(p2);
    }
}
//Id:1, Name:张三, Age:10
//Id:2, Name:李四, Age:12