Reference variable vs. Real object

This example shows what happens for the instance method, static method, variable in the inheritance.

======================== Code ========================
public class Sub extends Super{

int x = 15;
static int y = 25;
public static void main(String args[]){

//super reference and super object
Super t = new Super();
out.println(t.x + " " + t.y);
t.methodOne();
t.methodTwo();

//super reference and sub object
Super ts = new Sub ();
out.println(ts.x + " " + ts.y);
ts.methodOne();
ts.methodTwo();

//sub reference and sub object
Sub s = new Sub();
out.println(s.x + " " + s.y);
s.methodOne();
s.methodTwo();
}
static void methodOne() {out.println("Sub methodOne()");}
void methodTwo() {
out.println("Sub methodTwo()");
methodOne();
}
}

class Super{
int x = 10;
static int y = 20;
static void methodOne() {out.println("Super methodOne()");}
void methodTwo() {
out.println("Super methodTwo()");
methodOne();
}
}
================================================

======================== Answer ========================
10 20
A methodOne()
A methodTwo()
A methodOne()
10 20
A methodOne()
B methodTwo()
B methodOne()
15 25
B methodOne()
B methodTwo()
B methodOne()
================================================

======================== Conclusion ========================
static methods and variables are based on the reference type
Real object type determines which overridden method is used at runtime
================================================

SCJP

Those are my study note of the SCJP. I used those notes to prepare the SCJP exam. Wish myself have luck for the exam.


Uploaded on authorSTREAM by maggie.zhou





Uploaded on authorSTREAM by maggie.zhou





Uploaded on authorSTREAM by maggie.zhou





Uploaded on authorSTREAM by maggie.zhou

SQA

To understand what SQA doing, I create this note. The SQA is not same as quality control, it isn't testing. It is a process control to ensure the quality of software products. Hope my slides can explain the above points with details.




Uploaded on authorSTREAM by maggie.zhou

SQL

One of my study notes about SQL. It covers all the concepts about SQL syntax, database design, query, etc.


Uploaded on authorSTREAM by maggie.zhou

IPSec

I present the basic concept of IPSec. Let you know about what are differnets between the Transport mode and Tunnel mode, what are differents between ESP and AH, etc.

Uploaded on authorSTREAM by maggie.zhou

Ad hoc Network protocols

This note presents three important Ad hoc network routing protocol. These three protocol are the typical routing types which inspired other protocols. Once you understood these three, you will easily get the key point from others.


Uploaded on authorSTREAM by maggie.zhou

Lost root password in MySQL

If you lost the root password of MySQL, there are several to get over it. On Windows, you can use the following steps to reset a new password.

1. close currrent running MySQL: you can go to windows task manager(by press Ctrl+ALT+DEL), and end the process: mysqld-nt.exe

2, open a dos command window

3, set path as your mysql installation path, and into bin, mine is:

c:/program files/mysql/bin

4, Input command:

mysqld-nt --skip-grant-tables

if there is nothing shows up, it means everything is ok

5, Then, you need open another dos command window

6, Still, set the same path: c:/program files/mysql/bin

7, input:

mysql

then press ENTER key, to get into mysql

if you see:

mysql>

then so far so good

8. After the previous steps, please input:

use mysql;
update user set password=password("123456") where user="root";
flush privileges;

12345 is you new password for root user, please don't forget the semicolon and use double quote for both password and user name root

9. Quit mysql by input
\q

10, On Final step, you need to log out then login windows.

Now, you can use the new password to login mysql in the normal way.