5.23 面向对象案例分析五

• 用static ，引入计数器案例

class User {
    private String uid;
    private String password;
    private static int count = 0;
    public User(){
        this("NOID","mldn");
    }

    public User(String uid){
        this(uid,"mldnjava");
    }

    public User(String uid,String password){
        this.uid = uid;
        this.password = password;
        count++;
    }

    public static int getCount(){//--这里加上static,下面才可以不实例化,直接User.getCount来调用
        return count;
    }

    // getter,setter 略
    public String getInfo(){
        return "用户名：" + this.uid + ",密码:" + this.password;
    }

}

public class HelloWorld {
    public static void main(String[] args){
        User userA = new User();
        User userB = new User("小强");
        User userC = new User("大强","ican");

        System.out.println(userA.getInfo());
        System.out.println(userB.getInfo());
        System.out.println(userC.getInfo());

        System.out.println("已实例化用户个数:" + User.getCount());// 用户个数
    }
    
}

• 结果:

用户名：NOID,密码:mldn
用户名：小强,密码:mldnjava
用户名：大强,密码:ican
已实例化用户个数:3