Skip to main content

Java Core - Top 10 Questions Every Developer Should Know

#RandomlyPickedByMe

  • What is the difference between Javascript and Java?
  • Difference between StringBuilder and StringBuffer?
  • Why do I get "SomeType@a3fde" when I print my code?
  • Why is String immutable?
  • Why "equals" method when we have "==" operator?
  • Is List<Dog> a subclass of List<Animal>?
  • Why shouldn't we use raw type?
  • Is Java “pass-by-reference” or “pass-by-value”?
  • What's the advantage of a Java enum versus a class with public static final fields?
  • Why "double x = 0.1 + 0.2" and result of print(x) is 0.30000000000000004?

1. What is the difference between Javascript and Java?

Holy crap! (Vietnamese: Thế quái nào lại có câu hỏi ngớ ngẩn vậy chứ?)

"Java and Javascript are similar like Car and Carpet are similar." - Greg Hewgill (on StackOverflow)

2. Difference between StringBuilder and StringBuffer

String is immutable. StringBuilder and StringBuffer are mutable. StringBuffer is thread-safe. StringBuilder is modern than StringBuffer.

"As of release JDK 5, StringBuffer class has been supplemented with an equivalent class designed for use by a single thread, StringBuilder. The StringBuilder class should generally be used in preference to this one, as it supports all of the same operations but it is faster, as it performs no synchronization."
http://docs.oracle.com/javase/8/docs/api/java/lang/StringBuffer.html

3. Why do I get "SomeType@a3fde" when I print my code?

Because all classes extend the class Object which has the method toString().
public String toString(){
 return getClass().getName() + "@" + Integer.toHexString(hasCode());
}

4. Why is String immutable?

String s = "Hello";
s.replace("e", "E");
System.out.println(s); //"Hello"

s is only a reference to an String object "Hello";

5. Why "equals" method when we have "==" operator?

"equals" can be overridden, but "==" not.

6. Is List<Dog> a subclass of List<Animal>?

No. Because a List<Dog> is not a List<Animal>.

7. Why shouldn't we use raw type?

Runtime trouble, ClassCastException.

8. Is Java “pass-by-reference” or “pass-by-value”?

Java has only pass by value. A very simple example to validate this.
public void test() {
    MyClass obj = null;
    init(obj);
    //After calling init method, obj still points to null
    //this is because obj is passed as value and not as reference.
}
private void init(MyClass objVar) {
    objVar = new MyClass();
}

Imagine that likes the Shortcut (Reference) and the real file (object) in Windows. Shortcut can change content of its current point to but also can the reference to new file.

9. What's the advantage of a Java enum versus a class with public static final fields?

Consider the purpose! You should use enum types any time you need to represent a fixed set of constants such as the planets in our solar system. However, if we concerns technically the features between these; there are some more benefit when using enum: type-safe, singleton, switch case, built-in methods, etc.

10. Why "double x = 0.1 + 0.2" and result of print(x) is 0.30000000000000004?

Because double/float simply can't represent a number like 0.1.  This is caused by the way computers store floating-point numbers.
Detail: http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html

Reference:
[1]. https://stackoverflow.com/tags/java/info
Labels:

Comments

Post a Comment

Popular posts from this blog

Only allow input number value with autoNumeric.js

autoNumeric is a jQuery plugin that automatically formats currency and numbers as you type on form inputs. I used autoNumeric 1.9.21 for demo code. 1. Dowload autoNumeric.js file from  https://github.com/BobKnothe/autoNumeric 2. Import to project <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script> <script type="text/javascript" src="js/autoNumeric.js"></script> 3. Define a function to use it <script type="text/javascript"> /* only number is accepted */ function txtNumberOnly_Mask() { var inputOrgNumber = $("#numberTxt"); inputOrgNumber.each(function() { $(this).autoNumeric({ aSep : '', aDec: '.', vMin : '0.00' }); }); } </script> 4. Call the function by event <form> <input type="text" value="" id="numberTxt"/>(only number) </form> <script ty...
Post a Comment
Read more

Why Business Rules Engine Matter

"A good DSL minimizes the 'communication gap' between a domain concept and the code that implements it" - Robert C. Martin A Use Case It looks like adopting a new technology is always driven by a business need. The organizations, such as banks, have their own business processes (such as data gathering and document management). These processes are different from others but usually the differences are not big. How do we build a product which can be reused the similar features but still be adaptable with the specific requirements of each bank? Then, the answer is we should have a library/framework. There is an idea that we can implement this library/framework by using a business rules engine. Which has the following benefits: Be able to modify implementation of business domain at runtime (such as XML, CSV) S ource code is more readable for both developers and domain experts. Therefore, source code can be consider it as a document Since Business Rules Engine...
Post a Comment
Read more

The Evolution of Team Collaboration

I n my point of view, if a team has a good collaboration, team members will achieve the following: To be more effective To make work more enjoyable I have been working for a company for nearly four years as an software developer. Working on various projects from maintaining existing systems to developing a substantial product resulted in me moving to new teams three times. Actually, my most stable team lasted only around three years.  Every time I've moved to a new team, I have a chance to work with new members and a new team culture again. Indeed, I realize that there is a process of developing the team collaboration which gets better time by time. I think it is an evolution ! Phase 1: Poorly collaborate For example, that is when the team members have the following issues: Only work on his/her area of expertise Don't communicate to others Be not confident to take on new challages Don't listen to other members. Subsequently, the team ha...
Post a Comment
Read more

Building Axon.ivy Projects on Bitbucket Pipelines

Read me  if you don't know what Axon.ivy (Ivy) is. Motivation -  Ivy projects are designed to be built on a continuous integration (CI) server like Jenkins - Today, Bitbucket supports for CI with Bitbucket Pipelines - We're using Bitbucket. Then, why not? It must be very cool and convenient for us if we can centralize our CI and VCS (version control system) tools in one place. Here is an approach We have to use a maven plugin called project-build-plugin  to build ivy projects. This plugin requires an instance of Ivy engine during building time. Bitbucket Pipelines allows us to specify our own docker image as a build environment. What we need to do  is to prepare our docker image with needed stuffs such as JDK, Maven, Ivy engine, etc. Step 1. Prepare Docker images For testing purpose, I already created two docker images: Maven and Axon.ivy engine. They are now available on Docker Hub This image for Maven using Oracle JDK 8 This image for Axon.iv...
Post a Comment
Read more

Applying pipeline “tensorflow_embedding” of Rasa NLU

According to this nice article , there was a new pipeline released using a different approach from the standard one ( spacy_sklearn ). I wanted to give it a try to see whether it can help with improving bot’s accuracy. After applying done, I gave an evaluation of “tensorflow_embedding”. It seemed to work better a bit. For example, I defined intents “greet” and “goodbye” with some following messages in my training data. ## intent:greet - Hey! How are you? - Hi! How can I help you? - Good to see you! - Nice to see you! - Hi - Hello - Hi there ## intent:goodbye - Bye - Bye Bye - See you later - Take care - Peace In order to play around with Rasa NLU, I created a project here . You can have a look at this change from this pull request . Yay! When I entered message “hi bot”, then bot with “tensorflow_embedding” could detect intent “greet” with better confidence scores rather than bot with “spacy_sklearn”. The following are responses after executing curl -X POST loc...
Post a Comment
Read more