demo.java

我在学习JAVA的讲义

class RunDemo
{   private String userName,password;

    RunDemo( )
    {   System.out.println("All is null!");
    }

    RunDemo(String name)
    {   userName=name;
    }

    RunDemo(String name,String pwd)
    {   this(name);
        password=pwd;
        check( );
    }

    void check( )
    {   String s=null;
        if(userName!=null)
            s="userName:"+userName;
        else
            s="please input your password!";
        if(password!="ThisWord")
            s=s+"  invaid!";
        else
            s=s+"  password:********";
        System.out.println(s);
    }
}

public class Demo
{   public static void main(String args[ ])
    {   new RunDemo( );
        new RunDemo("Bill");
        new RunDemo(null,"Bill");
        new RunDemo("Bill","ThisWord");
    }
}