总结

案例

要求

代码：

User类：

package com.day1_static;

public class User {
    public static int num;

    public User() {
        User.num++;
    }
}

Test类：

package com.day1_static;

public class Test {
    public static void main(String[] args) {
        User user1 = new User();
        User user2 = new User();
        User user3 = new User();
        System.out.println(User.num);

    }

}

运行结果