Interview questions

These are few interview questions asked. The questions are based on Java and non technical. Some of the questions seems to be very simple and staight forward.

1. what is the difference between comments in java

Ans: 3 types of comments in java

a. // - which is single line comment
b. /* */ - which is to add a comment of more than one line, we can precede our comment using/*
c. /** */ -multiple line comments. Used for documentation purpose.

2. when there is a problem with the application, as a developer where we need to look at.

Ans : error logs and application server log files

3. How do you avoid deadlocks in a multithreaded enviornment?

Ans : first approach try to avoid synchronized where ever possible. If it is unavoidable, then code in such way that each thread should get lock & unlock in the same order or squence.

4. Write a Java program that:

- inputs a String from a user. Expect the String to contain spaces and alphanumeric characters only.
- capitalizes all first letters of the words in the given String.
- preserves all other characters (including spaces) in the String.
- displays the result to the user.

Answer : *
Approach : I have followed a simple approach. However there are many string utilities available
* for the same purpose. Example : WordUtils.capitalize(str) (from apache commons-lang)

/*****************************************************************************/
public static void main(String[] args) throws IOException{
System.out.println("Input String :\n");
InputStreamReader converter = new InputStreamReader(System.in);
BufferedReader in = new BufferedReader(converter);
String inputString = in.readLine();
int length = inputString.length();
StringBuffer newStr = new StringBuffer(0);
int i = 0;
int k = 0;
/* This is a simple approach
* step 1: scan through the input string
* step 2: capitalize the first letter of each word in string
* The integer k, is used as a value to determine whether the
* letter is the first letter in each word in the string.
*/

while( i < length){
if (Character.isLetter(inputString.charAt(i))){
if ( k == 0){
newStr = newStr.append(Character.toUpperCase(inputString.charAt(i)));
k = 2;
}//this else loop is to avoid repeatation of the first letter in output string
else {
newStr = newStr.append(inputString.charAt(i));
}
} // for the letters which are not first letter, simply append to the output string.
else {
newStr = newStr.append(inputString.charAt(i));
k=0;
}
i+=1;
}
System.out.println("new String ->"+newStr);
}
}
/*****************************************************************************/

5. How to reverse a string?

InputStreamReader inst = new InputStreamReader(System.in);
BufferedReader in = new BufferedReader(inst);
StringBuffer input = new StringBuffer(in.readLine());
System.out.println("Input String-->"+input);
System.out.print("reverse String-->");
System.out.print(input.reverse());

6. Palindrome program.

InputStreamReader instr = new InputStreamReader(System.in);
BufferedReader in = new BufferedReader(instr);
StringBuffer input = new StringBuffer(in.readLine());
StringBuffer reverseStr = new StringBuffer(input.reverse());
String inStr = input.toString().trim();
String outStr = reverseStr.toString().trim();
System.out.println(reverseStr);
if (inStr.equals(outStr)) {
//if (input.length() == reverseStr.length()) {
System.out.println("Palindrome");
//}
} else {
System.out.println("not Palindrome");
}

7. How does equals() method differs for String and StringBuffer classes?

String.equals() compares the 2 strings whereas StringBuffer.equals will return true only if compared with itself.

for comparision of strings we must use String.euqals() method or convert the StringBuffer to String and then compare.

Deploy a JSP in WebLogic 10.3.4

Easy Steps :

1. Place the JSP in a new folder say Temp.

2. Create the war file using the command - jar -cvf TestJSP.war myJSP.jsp

3. Upload this war file from the weblogic deployments console
4. Access the JSP with URL - http://localhost:7001/TestJSP/myJSP.jsp

org.hibernate.QueryException: ClassNotFoundException: org.hibernate.hql.ast.HqlToken

This is in sequence to my earlier post.

There are 2 ways as given below. But in my environment , I had to apply both the following steps as solution for above issue.

1. Changes in weblogic-application.xml

Add the antlr.* in the tag
----------------------------------

<prefer-application-packages>
        <package-name>antlr.*package-name>
    prefer-application-packages>

-------------------------------------

2. Changes in weblogic.xml

----------------------------------------
WebLogic has it's own version of ANTLR. Set the prefer-web-inf-classes element in weblogic.xml to true.

<weblogic-web-app>
  ....
  <container-descriptor>
    <prefer-web-inf-classes>trueprefer-web-inf-classes>
  container-descriptor>
  ....
weblogic-web-app>

------------------------------------------------

**** take care of the closing tags in the above XMLs by opening the XML file in any browser.

SCJP 6

here are certain links for mock exams to prepare for scjp 6.0

1.http://faq.javaranch.com/java/ScjpFaq
2. http://faq.javaranch.com/java/ScjpMockTests
3. http://examlab.tk/

Examlab is tough, but if you get 50% of score, then it is almost sure that you can pass the SCJP

All the very best!!

ICICI has removed the NEFT charges & HDFC introduced NEFT charges:)

Finally ICICI Bank not charging for the online transactions. That is good news for this new year!!!

But HDFC introduced the NEFT charges....

Real Estate comparison in Bangalore and Trivandrum

This is a just my observation about the real estate market in Bangalore and Trivandrum. I recently bought a plot in Bangalore !( can not say it is in Bangalore as the place is very far away from Bangalore city.)

I purchased a 2064 sq ft in xxxxhalli :-) in Old Madras Road. It is very near to the Volvo factory in Bangalore. It cost me around 9 lacs. I am not sure whether it was a good deal or not. But later I found that the local people sold that area to the builders for about INR 225 per sq ft. This is a rough calculation. But having said that, I am getting the advantages of a fully built Township features at my place. So I am consoling myself. :)

I bought a flat in Trivandrum in 2008. It is a 3 BHK & cost me 34 lacs. Again at that time I was hoping to increase the price of flat in future, but now if I buy the same flat, there is hardly any change in price or no change.

But at that time I had inquired the price in Bangalore as well. The price is drastically changed during these period.

But I know that the market value for a city like Bangalore is nothing comparable to Trivandrum and again I will say that it is good that the flat price has not come down in Trivandrum even at the rescission time:)

What is the use of setting SerialVersionUID in serialization?

The serialVersionUID is a universal version identifier for a Serializable class. Deserialization uses this number to ensure that a loaded class corresponds exactly to a serialized object. If no match is found, then an InvalidClassException is thrown.

Guidelines for serialVersionUID :

* always include it as a field, for example: "private static final long serialVersionUID = 7526472295622776147L; " include this field even in the first version of the class, as a reminder of its importance
* do not change the value of this field in future versions, unless you are knowingly making changes to the class which will render it incompatible with old serialized objects
* new versions of Serializable classes may or may not be able to read old serialized objects; it depends upon the nature of the change; provide a pointer to Sun's guidelines for what constitutes a compatible change, as a convenience to future maintainers

In Windows, generate serialVersionUID using the JDK's graphical tool like so :

* use Control Panel | System | Environment to set the classpath to the correct directory
* run serialver -show from the command line
* point the tool to the class file including the package, for example, finance.stock.Account - without the .class
* (here are the serialver docs for both Win and Unix)

readObject and writeObject :

* readObject implementations always start by calling default methods
* deserialization must be treated as any constructor : validate the object state at the end of deserializing - this implies that readObject should almost always be implemented in Serializable classes, such that this validation is performed.
* deserialization must be treated as any constructor : if constructors make defensive copies for mutable object fields, so must readObject
* when serializing a Collection, store the number of objects in the Collection as well, and use this number to read them back in upon deserialization; avoid tricks using null

Other points :

* use javadoc's @serial tag to denote Serializable fields
* the .ser extension is conventionally used for files representing serialized objects
* no static or transient fields undergo default serialization
* extendable classes should not be Serializable, unless necessary
* inner classes should rarely, if ever, implement Serializable
* container classes should usually follow the style of Hashtable, which implements Serializable by storing keys and values, as opposed to a large hash table data structure


/**
* Determines if a de-serialized file is compatible with this class.
*
* Maintainers must change this value if and only if the new version
* of this class is not compatible with old versions. See Sun docs
* for * /serialization/spec/version.doc.html> details.
*
* Not necessary to include in first version of the class, but
* included here as a reminder of its importance.
*/
private static final long serialVersionUID = 7526471155622776147L;




[Post New]posted Monday, May 09, 2005 10:44 PM private message
Quote [Up]
*g* as you mention "Java RMI"... it says:

"The downside of using serialVersionUID is that, if a significant change is made (for example, if a field is added to the class definition), the suid will not reflect this difference. This means that the deserialization code might not detect an incompatible version of a class."

and furtheron suggests to implement readObject & friends and writing a version "manually".

All this in order to gain performance:

"Setting serialVersionUID is a simple, and often surprisingly noticeable, performance improvement. If you don't set serialVersionUID, the serialization mechanism has to compute it. This involves going through all the fields and methods and computing a hash. If you set serialVersionUID, on the other hand, the serialization mechanism simply looks up a single value."