Category: Software development

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Tree data structure is fairly common in software development, and luckily I have quite a bit experience working on those in my career. I started working on this as I was working for UGS/Siemens PLM Software, and I was involved in the development of XML based data adapter for CAD data exchange, a key piece of information we want to translate is the assembly information, or product structure, or in computer/software terms, the tree hierarchy. I did learned a few things on recursive function, etc. Interestingly enough, later on I got a interview phone call from Google, and the guy asked me about recursion, for a simple problem like this: basically they are 100 matches, every time one can take one or 2, how many combinations are there? I said let’s do it in recursive fashion, after quite a bit reminder/hint, finally I said n(100) = n(99) + n(98)

But they were not very impressed with me, as I did not come up with the solutions fast enough, which is fine. I am who I am, I can work on those kind of interesting problems, in my own pace. Or explained in my Chinese name, it’s getting faster gradually 🙂

My dumb mistake

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(Update 02-19-2021)

spring.io Testing the Web Layer

Mockito Example with Best Practices

JUnit and Mockito : Best Practices, Do’s and Don’ts

(Original) Test Driven Development (TDD) is getting popular these days. I had opportunity to being exposed it recently. I am not new to unit test. In the software company I worked for 8 years, we have regression test suites that runs automatically (at least daily), and we update the test suites as we find edge cases from customer bug reports, or in our development. That was about 8 years ago. Since the switch into Java land (2010), I started using JUnit and create/run the unit tests. One thing I was exposed to recently is Mocking in unit test, and TDD. Both takes a little time, and I am not fully bought into TDD yet. But I did learned something interesting on both topics lately, and like to share.

1) TDD
One of my coworker is very experienced and in-grained in this, as we are doing pair programming, I learned this a bit. An interesting back and forth as I was making changes to a method.

Coworker: “Do you have a test case?”
Me: test case for what?
Coworker: for the change?
Me: do we need this? …

But eventually we wrote the case, magically the web app also worked as soon as we passed the unit test. But overall I still have some reservation to do this, as I am not good at mocking e.g. Mockito, or writing test, and I think there is some cases pair programming can get the code right without go heavy in unit test.

Some links for mockito and spring test

Stubbing and Mocking with Mockito and JUnit

https://www.vogella.com/tutorials/Mockito/article.html
https://stackoverflow.com/questions/39486521/how-do-i-mock-a-rest-template-exchange
https://www.baeldung.com/spring-mock-rest-template
https://stackoverflow.com/questions/11969609/junit-mockito-when-thenreturn-throws-nullpointerexception/18060451
https://javacodehouse.com/blog/mockito-tutorial/

2) Unit test (auto test suites)
I heard from my coworker recently that test suites should not use the implementation data source (database). I thought the main reason is the heavy weight/use from database resources point of view. But there is more, today I found if auto test consistently changes things on dev database, it’s really hard to find out the root cause, and cause confusion. Initially we thought the problem was caused by batch job, or the web app, spent a lot time trying to figure out, both are not the cause. And luckily, at the end we were able to find out the real cause.

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This is the common saying I heard a lot when I started worked for a software company on development. I can list some of the pros and cons of fix it.

Pros
Architecture chaos: if not fixing it, basically as the software ages, per the “broken windows” theory, people would just throw in changes to get things done, without carefully thinking about the architecture, dependencies. And this leads to the related problem below.

Code hard to maintain: it will become harder and harder to fix bugs, or add new features with the code in a messy state.

Cons
Introduce new bugs by accident. Or the fix making the software worse. While it’s unlikely, it’s still possible. Not carefully planned fix could introduce bugs, and make the software worse. I have done my share of that too 🙁

Refactor
If we were to work on the clean up, refactor the code, as a minimum we should have the regression test suites. Or in ideal world, we would have automated unit tests, which could help both speed up development, and give another level of confidence for the code change.

Reading Time: 2 minutesIn my 13+ years of software development career, I have done both. So which one do I prefer? This is a bit like asking my daughter: who do you like more, mommy or daddy? (I will reveal my daughter’s answer at the end.)

I think both are interesting work, and both could be challenging. If you ask me pick one, I will probably pick the new development, as most developers like to work on new things: from new technologies to new features, new project/product. But from time to time, I have worked on some bug fixing work that is not only interesting, but also challenging and rewarding (mentally not financially, as I worked for companies all these years). I recall 6, 7 years ago, when I was working for CAD software company, we had two bugs to fix, the first one is actually not too bad, essentially it’s a tolerance problem. In other words, I just need to make sure when it checks whether the X, Y, Z axis is orthogonal to each other, I gave some tolerance. I did cross products of vectors, borrowing from similar experience I learned at work.

The second one, is a bit daunting, to say the least. Essentially we have about 2 weeks to fix a nasty problem in a CAD translator, and we don’t have any clue why the results is wrong. By working with 3rd party, and looking carefully at the problem, some teamwork, I was able to solve the mystery when I was working remotely at Shanghai. I recall I could not fall asleep that night, as I knew that’s a tough problem and will help the sales team greatly to sell into a top Europe car maker.

I had similar experience most recently, although it’s a totally different problem, and we as developers also work in much different world: with stackoverflow.com, and google search (blogs).

So back to my daughter’s answer to my silly question: most of times she will say mommy and daddy; sometimes she will say “don’t ask silly questions”.

PS: in some places bug fixing is also called as maintenance. Just like the car maintenance, software also needs regular check-up and fix 🙂

Reading Time: < 1 minuteI need to do some development work on Windows, using Visual Studio. I like to have a simple source code control system, in recent years I have used CVS, Subversion and git (on Mac). I did a google search on Subversion and found some instructions regarding setting up Subversion.

Setting up Subversion on Windows

and this one

Installing and Configuring SVNServe and TortoiseSVN on Windows

Download/install the SVN server and starting the windows service was relatively straightforward. So as the Tortoise SVN client. Couple things keep in mind:

1) Some sites requires registration or install additional software, I chose sites that does not require registration.

2) I found sometimes I can not open up svn://localhost successfully, in the same command prompt window where I start the SVN service. After I close the command prompt and tried again, it worked. The commands I used are:

set SVN_EDITOR=c:\windows\system32\notepad.exe
svn mkdir svn://localhost/myproject

Reading Time: 4 minutes(Update 02-27-2019) It’s 5 and half years since last update. And two more jobs for me :] Noticed from recent job search in STL, code exercise and code testing (at the spot, pair programming, TDD) is becoming common now in STL, which is unthink of 5.5 years back. I did add a few blog posts on this fronts recently.

Javascript jasmine node.js based testing

Code exercise : linear chamber animation / simulation

Spring, Spring Boot and React

Also, on pure concepts side, Java (J2SE) and J2EE (Spring and Hibernate) are still important and questions were asked around both areas too.

Example questions:
JPA annotations
Hibernate configuration (XML file)
OOP Concepts
Java Interface vs Abstract class (do we need to implement abstract method to use the class)
final finally finalize java
spring model view controller annotation
classpath loading

(Updated 08-31-2013) For those brave hearts venture out the silicon valley/seattle, here is the must-do homework (LeetCode). Chinese version (here and here).

(Original)
Oracle
SQL: Inner join and out join

Function, (stored) procedure and package

What is a trigger in Oracle

“…Oracle lets you define procedures called triggers that run implicitly when an INSERT, UPDATE, or DELETE statement is issued against the associated table or, in some cases, against a view, or when database system actions occur. These procedures can be written in PL/SQL or Java and stored in the database, or they can be written as C callouts.

Triggers are similar to stored procedures. A trigger stored in the database can include SQL and PL/SQL or Java statements to run as a unit and can invoke stored procedures. However, procedures and triggers differ in the way that they are invoked. A procedure is explicitly run by a user, application, or trigger. Triggers are implicitly fired by Oracle when a triggering event occurs, no matter which user is connected or which application is being used…”

A shorter version at orafaq forum

Longer version at orafaq.com/wiki

7. Compare and contrast TRUNCATE and DELETE for a table.
Both the truncate and delete command have the desired outcome of getting rid of all the rows in a table. The difference between the two is that the truncate command is a DDL operation and just moves the high water mark and produces a now rollback. The delete command, on the other hand, is a DML operation, which will produce a rollback and thus take longer to complete.

8. Give the reasoning behind using an index.
Faster access to data blocks in a table.

11. Give some examples of the types of database contraints you may find in Oracle and indicate their purpose.
A Primary or Unique Key can be used to enforce uniqueness on one or more columns.
A Referential Integrity Contraint can be used to enforce a Foreign Key relationship between two tables.
A Not Null constraint – to ensure a value is entered in a column
A Value Constraint – to check a column value against a specific set of values.

DDL vs DML
Data Definition Language (DDL) statements are used to define the database structure or schema. Some examples:
CREATE – to create objects in the database
ALTER – alters the structure of the database
DROP – delete objects from the database
TRUNCATE – remove all records from a table, including all spaces allocated for the records are removed
COMMENT – add comments to the data dictionary
RENAME – rename an object

Data Manipulation Language (DML) statements are used for managing data within schema objects. Some examples:
SELECT – retrieve data from the a database
INSERT – insert data into a table
UPDATE – updates existing data within a table
DELETE – deletes all records from a table, the space for the records remain
MERGE – UPSERT operation (insert or update)
CALL – call a PL/SQL or Java subprogram
EXPLAIN PLAN – explain access path to data
LOCK TABLE – control concurrency

1. Describe the difference between a procedure, function and anonymous pl/sql block. Candidate should mention use of DECLARE statement, a function must return a value while a procedure doesn?t have to.

PL/SQL developer vs. Toad

Reporting
SQL Server Reporting Services (Microsoft); SQL Server Reporting Services (wiki)

Oracle 10g reports (PDF); Oracle Reports Tutorial

LIMS (wiki)

Java
(Updated 08-31-2013) OOPS Interview Questions

Top 20 Core Java Interview questions answers asked in Investment Bank

(Original) 30 Core Java questions (sys-con)

J2EE interview questions (techInterviews.com)

more j2ee interview questions

Java: hashMap and hashTable

Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones.

Difference between Get and Post method on web (link one)

Lazy initialization, dependency injection

3 Things in OO:
data encapsulation, polymorphism, dynamic dispatch (when a method is invoked on an object, the object itself determines what code gets executed by looking up the method at run time in a table associated with the object. This feature distinguishes an object from an abstract data type (or module), which has a fixed (static) implementation of the operations for all instances. It is a programming methodology that gives modular component development while at the same time being very efficient.)

How to use static method? (Include class name)

Aggregation

Throwable interface (exception)

What is reflection

Interface vs. abstract class
non-static method
final: immutable, e.g. String
finalized method

tree-reflection