构造方法的重载

构造方法也是方法，也可以重载；

public class User {
    int id;
    String name;
    String pwd;

    public User() {

    }

    public User(int id, String name) {
        this.id = id;
        this.name = name;
    }

    public User(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    public static void main(String[] args) {
        User u1 = new User();
        User u2 = new User(101, "张三");
        User u3 = new User(102, "李四", "123456");
        System.out.println(u1);
        System.out.println(u2);
        System.out.println(u3);
    }
}